1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

hogged out vs boost prepped (Nikki)

Old 09-04-15, 04:06 PM
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hogged out vs boost prepped (Nikki)

There were two schools of thought when it came to modding Nikkis.

One way is to try to reduce as many air restrictions as possible for NA use because a CFM gained is a CFM earned. This is simply due to the way you have to make power using only atmospheric pressure and engine vacuum. This was Yaw's and Sterling's way; make the carb as free flowing as possible with some compromises along the way. It worked, more or less.

The other way is to leave the carb's internal parts alone aside from maybe a secondary jet change, and force feed it with a turbo. This was bad_83's and Robert's way, which also worked, more or less.

I'd call these two schools of thought definitely old school. It relates to a time when we didn't really know all that much about these carbs, and it shows if you go back and read posts from ten years ago. We were such noobs!

Since then, I think we've come a long way. Or at least I have in my understanding of these carbs.

Over the last year and a half, I've figured out ways to successfully marry the two disciplines into one hogged out boost prepped Nikki that actually works. I've improved on everything previously done to these carbs, and streamlined the process while deleting/recommending against unnecessary or in my opinion misguided mods done by others that can potentially hurt the carb or the engine.

My carbs offer the flow you need for NA and the air bleeds and safe tuning that work with boost. It handles a full power run breaking them loose in gear on dry road (in my car anyway), then returns to idle like nothing happened. No more flooding! No more secondary delay! It just works!

This is not an advertisement, by the way. Think of it as an informative thread filled with valuable information should you choose to mod your own carb. Not a step by step how-to guide, but rather a path to follow and steps to avoid. I also don't keep secrets. Feel free to ask away and I'll answer as well as I can. My reasons are to keep as many of these on the road without resorting to fail injection.

In modding these carbs, there are things to avoid:

Absolutely DO NOT change out the OEM needles and seats, or adjust the floats. It is well known by now that EVERY aftermarket rebuild kit contains incorrectly machined seats that flood every time. This problem is industry-wide. Only factory seats (expensive) should ever be swapped in if you need them new.

I like to pull the stock strainers to increase fuel flow for boost. I remove the stock seats using a vice grip because they were tightened 30 years ago and require a shock to free them up. Hitting the vice grip with a hammer works every time. The aluminum crush washer is usually very crushed and you will tear out the slot in the seat if you apply a lot of torque with a wide screwdriver. Only use the wide screwdriver to reinstall the OEM seats using new crush washers from the rebuild kit. Get them tight but not to where you tear the slot out the other direction. I accidentally did that once.

Absolutely DO NOT cut/shorten the OMP nipples/tubes like Yaw and Sterling. This was a misguided way to try to get more CFM. The reality is once you enlarge the venturis, the restriction caused by the OMP tubes is inconsequential and cutting them prevents the oil from running down the outside of the booster and mixing with the fuel as Mazda intended. What happens instead is a large amount of oil builds up along the upper ridge and then will occasionally drool down along the wall of the venturi. This can lead to premature apex seal wear and makes the upper part of the carb's primary side really dirty, really quickly. You'll see this if you have a Yaw or Sterling with this crappy mod. See if you can tap them in deeper or find some stock ones to swap in. Sorry, I can't help you out because I'm short on these myself so don't ask.

Do not drill out your jets or air bleeds with a 1mm drill bit. This kills your tip-in and leads to a rich condition. I know this info has been on the forum for a while but it was posted by someone who honestly didn't know what he was talking about. Air bleeds don't really function that way anyway. It seems Carl himself didn't really understand them as can be discerned from reading his posts from years ago. If Carl didn't, Sterling didn't either.

I've found the perfect air bleed size to be stock 70. I've tried 60, 70, the rare 80 and the common SA 90. 90 was terrible and didn't allow the carb to run much past 5 or 6 grand with hogged out venturis and boost. The 80 was a little better but 70 was the best. The 60 caused a glitchy or unsmooth condition which only improved when I drilled it out with a micro drillbit to .68mm because this was the closest size to .70mm I had without going over. And it turns out that the OEM 70s are closer to .68 anyway so win-win.

So with all that now out in the open, I'd say the Yaw and Sterling tuneable primary air bleeds are unnecessary. Unless you only have 90 available. But then I don't recommend modding an SA carb anyway. Too many issues with those. But if you must, use one, I'd recommend machining the 90s to swap in a .68 drilled Hitachi pilot jet or maybe a holley dominator air bleed in whatever SAE size gets it close.

However I DO NOT recommend those holley air bleeds as fuel jets due to their inferior funnel shape which, it turns out, leads to a cornering problem that apparently was a real problem with Sterling carbs, and he never figured out why! I think even Yaw carbs had this issue and he or Sterling were recommending a swap to RX-3 full size floats and Grose jets in a misguided attempt to solve a problem caused by their poor "jet" choice. I recall Sterling was even considering a baffle in the float bowl. While a good idea in principle, in reality it was a band-aid to cover for incorrect parts mimicking jets.

Another thing I dislike about the holley dominator air bleeds are the huge gaps between sizes, not to mention that they're in SAE even though our carbs are metric. I understand you probably grew up with imperial measurements like Yaw/Sterling and find them easier to deal with, but the honest truth is working with actual metric numbers is FAR easier than dealing with decimals of an inch or whatever. Plus the way they're made is pretty sorry in my opinion. Chips of brass that you need to clean off yourself. Terrible. I've seen some where the holes weren't even drilled straight. Awful.

I also don't recommend the expensive weber jets that Mazdatrix sells because not only are they way too expensive, they also have the inferior funnel shape and are stepped every .05mm which I've found is too wide for fine tuning. I prefer .02 such as found at jetsrus or .03 at the most from my micro drillbits. Hey, I've got a wideband. I'm going to use it!

The only gaskets in rebuild kits I've found that actually work are for the air horn and, for 82 and older carbs, the float bowl vent solenoid gasket. All others in the kit are junk. And even the air horn gasket requires careful trimming inside the screw holes and around the seat area. Really misaligned holes, but they are usually thick paper and take a nice crush and don't leak much under boost. Don't try to use RTV or some other sealant here. You're just making your life harder, and the gasoline will find a way to seep out anyway. I've never done this, but others have mentioned possibly doing it. Please don't.

Use the thin gasket that goes between the main body and baseplate as a template on a piece of thick paper. I like to use the blue paper that comes in a kit from your local auto parts store. It's meant for waterpumps but seems to work ok for the baseplate and doesn't cause boost leaks. It take a bit of work to cut it all out with an xacto knife or whatever, but if you only have one of these to make, it's not a problem.

Use the slightly thinner gray paper for accel pump gaskets. I follow Sterling's old original accel pump mod instructions where you place three gaskets on either side of the accel pump diaphragm, using it as a template and cut out the 6 gaskets. I also found recently that the steel extension piece must have a hole spacing of 1 1/4" just as he recommends (I've tried different spacings but 1.25" is best) but I oval both holes now so I get some fine adjustment. Works great! Please search the forum for the how-to on the AP mod as he called it.

DO NOT do the Sterling flip-o-matic for mechanical secondaries. Again a misguided reinvention of the wheel we all seemed to be into some ten years ago, thinking we could do things better than Mazda. I saw, on Jingkun's carb, that it opened the secondaries too far and they actually would flow less! Terrible mod that is easy to get wrong. Instead, you can wire tie the linkage or what I prefer, is a tack weld. Hey, with boost, I feel it's necessary, you know? And it's the type of mod that will never fail.

DO NOT thin the throttle shafts!!! I know some of you out there have done it. Yaw and Sterling did it, and then require you to add some kind of pedal stop to your car to keep from twisting the shaft. Again a misguided attempt to improve air flow for NA use with proven CFM numbers blah blah blah. All this does is weaken the shaft and "hurts the carb" in my opinion. For boost, it's a big no-no. And even for NA use, I would never do this mod. I justify my position by saying I could almost get the tires to break loose in 1st gear on dry road, in a straight line going up a hill. The right rear was loosing grip but the LSD was transferring power to the left wheel, causing that "almost gonna break it loose, but not quite there" effect. I'm sure we've all been there. If that's not powerful enough for you, then obviously you need a turbo.

Any other do nots I can mention? Oh there is something about the primary short slow bleeds being way too big from the factory for anything other than stock 20mm venturis with a choke flap valve. And even then, the carb can be improved with smaller ones. The factory sizes ranged from 150 to 190 with the majority of FB carbs having 170. I've found that any kind of venturi work with a choke flap removal requires something smaller swapped in. I've had the most success with a 118 drillbit (.0456" which is a common size to find). But you can't drill it to a smaller size, unless you know some trick with metal the rest of us don't. So I recommend pulling the secondary short slow nickel plated 60s, drilling them to 118, swapping in to the primary side and then filling the stock 170s with solder and drilling them out to .37mm and installing in the secondary side. You MUST have at least some air flow here to break a siphon effect produced when you floor it and let off. The siphon pulls all the fuel out of the bowls through the secondary jets and floods the barrels faster than fuel can flow in at 2.5psi. This effect only ends when the bowls run out of fuel and air is sucked/introduced. If it happens while driving, it can take 1/8 to 1/4 mile to subside. So you HAVE TO have a small hole to break the siphon before it can get started which the factory determined to be .60mm. However that is relevant to a lazy NA setup with factory vacuum secondaries. I noticed the secondary delay was slightly longer with nickel plated 60s so I experimented with the smallest drillbits I had. I tried .25mm which worked but was too small and easily broke off inside of one later on. .35mm seemed to work but eventually broke off inside the solder as well so I switched to the next size up I had at .37mm. So far so good and the secondaries have been flood free ever since.

I suppose another option for some of you would be the leave the nickel plated 60s alone and solder fill the 170s, then drill to 118 and install back in the primary holes. Just an option if you find your secondary delay to be smaller than mine was. But watch for tin whiskers/solder bloom inside the hole!

Solving the secondary delay required me to jump through several hoops before I nailed it. And by solved I mean drive it's just like any other mechanical secondary carb. But, and you know where I'm going with this, if you floor it too soon it'll bog, right? Actually no! I've found if I floor it too soon, it doesn't bog but it doesn't make any additional power either. In other words, it doesn't upset the carb like a typical mechanical secondary carb would be. Instead it just sounds a little more throaty. This is due to the other secondary air bleeds I changed/modded. Here is a quick list of stock vs my modded ones:

stock secondary:
140 main air bleed
open long slow bleed
short nickel plated 60 slow bleed

modded secondary:
80 main air bleed
solder filled long slow bleed
solder filled primary short 170 slow bleed drilled to 37

This speeds up the how fast the secondaries come on line and gets rid of the bog at anything lower than 3000. If you floor it at 3000, it has been described as a transcendent experience. If you wait to floor it after 3000, this is where a lot of my trouble with the secondary delay was coming from. However these days I've gotten it so short that it only lasts for 1/8 to 1/10 of a second up there. Just a tiny glitch, if you will. But who really waits until 5 or 6 grand to floor their car anyway? I only did it while testing the primary circuit's AFR. But if you're trying to accelerate like a normal person, you'll tend to floor it sooner, right? But again being a mechanical secondary carb, you will want to wait until 3000 before you floor it. Or there a bouts. My setup likes 3000 and has a leaky brake booster so if I can compensate for that, holy crap just think of how much less time your secondary delay will take without all that unwanted air flowing into the secondary runners!

And you can always play around with your secondary main air bleeds. I've found I can't go smaller than 80 on my main secondary air bleeds. Any smaller and it has glitches. Any bigger and the delay gets longer. So 80 is like right at the knife's edge of perfect. Again because my brake booster has a small leak, I am getting slightly more secondary air than I'd want. But the nice part is if you start out with 80 drilled air bleeds, it's pretty easy to drill them out larger. Just don't go any larger than stock 91 or 92 primary jets because you're better off swapping a set of those in instead of drilling the 80s out to that size. Again, you just gotta play around with it. Every setup is different.

As for the long slow bleeds I fill with solder, these were only useful in a stock carb with vacuum secondaries and must be filled with solder to be used with mechanical secondaries. Sterling had to come up with his "AP mod" to try to cover for them by providing plenty of fuel for when they would be forced open by your foot, to get over the sudden rush of additional air, not when a team of engineers determined, through drilled orifice size and thousands of hours of testing, when they should open, and made sure conditions were right so as not to get a bog, and all that.

The long slows set when and where in the load vs RPM range the secondaries will open and how fast they come online. They're kind of the transition circuit of the secondaries. In other words every other circuit has produced an ideal mixture already including them to some extent, so the secondaries are perceived as a smooth rush of power that isn't really all that noticeable when they open. Boring.

But you have to understand my first experience with secondaries on a rotary was an old school RB Holley 550 in a REPU that had a screw jambed into the secondary linkage. This caused a secondary delay, but then when they'd come online, you could almost hear the right rear tire breaking loose on dry road. An early transcendent experience, if you will. It's what hooked me on rotaries.

So I like it when the secondaries kick in hard and fast and throw you back in the seat without any delays, glitches, bogs, or hiccups. I know factory setups aren't like this, and that's shame. But more awesome for us, I guess.

Wow, I typed a lot. There is more to talk about, but I'll leave it here for now.
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mschiap (10-01-17)
Old 09-06-15, 12:40 PM
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I was just reminded yesterday, that most Nikki owners who have the basic mechanical secondary mod requires you to wait until about 4000 RPM before you can floor it. Otherwise you experience a bog. Yes, an actual bog! It has been so long since I experienced this, I had forgotten about it. Interesting.

My one and only experience with the secondary bog was on the first Nikki I ever did anything with in late 2004. It was a nice low mile 84-85 that only had the main bulk of the complicated choke stuff removed. Mostly everything else was there. I removed the altitude compensator and a few other things, and gave it the accel pump mod and wired the secondaries for mechanical. I finally got to test run it for the first time in 2006 when I had access to a 12A. This carb ran pretty well but didn't have any low end torque due to its stock 20mm venturis. The 12A was 74 ported and the exhaust was the RB long primary with a light steel flywheel. It was painful waiting until 3800 (the lowest I could floor it at) before I could open the secondaries! And with what Sterling kept posting on the forum in those days, I was convinced that there wasn't any other way so I wasn't even looking.

Of course the truth is with air bleed tuning, the secondary bog at about 4000 and lower has been eliminated! The low end torque has also been vastly improved! These two improvements happened not from following Sterling's advice, but rather seeking to make the carbs work better with boost. These improvements happened almost by accident.

You see, if I had only ever followed Sterling's and Carl's advice, I would never have ventured into venturi cutting and air bleed tuning because as every knows from reading their posts, there is nothing to be gained from increasing venturi size out beyond his textbook perfect 22mm. He even stated that the raw size is not as important as the shape. He insisted that his perfect venturis cut with his lathe after much extensive trial and error test cuts and then flow bench testing done by Carl, provided the highest vacuum signal and that no amount of air bleed or jet tuning will ever cover for or correct the AF curve from a set of hand-cut venturis like mine. Um, sorry guys, but my AF curve is healthy enough to keep an engine alive up to 8 grand in boost with good numbers on the wideband. Your carbs didn't even work with any kind of boost, let alone keep a healthy AFR with it. And I didn't have to do all the weird mental gymnastics you guys apparently had to do to get there. All the posts on the forum but with little to show for it. Or something. I don't know what you guys were on, but what I do know is my carbs work and I know why they work.

peejay shed some light on the Sterling carb problems earlier this year. He said it had something to do with the strong reversion pulses these engines have, and how the starting and stopping of flow combined with tiny stock 20mm venturis was not allowing them to make any low end torque because as soon as the port runner starts to flow the right direction, it changes direction and flow is halted. Larger venturis help with this problem. This could be why I've had such tremendous results going with venturis of a size that any Sterling and Carl follower would cringe at. Of course I've got a 13B, which is another issue the personality cult followers would probably cringe at. Maybe. It is a bigger engine after all, but it is in a GSL-SE. But let's not lose focus.

By personality cult followers I'm talking about those who are easily swayed by strong personalities who use flowery language and faux physics. By faux physics I'm talking about how a flow bench is the same thing as an actual carb on an actual engine, and how the similarities are undeniable.

Do you see what I'm getting at? It should be all about field work, which is what I do. When Sterling stopped test driving and even test running all of his later carbs, it was bound to catch up to him. You don't run a carb customizing business like that. It's as bad as the waterbed salesman who sleeps on a coil spring mattress! No wonder all of Sterling's later carbs couldn't even idle. He never figured out why that happened. All he did was throw a set of nickel plated 60s in the primary side and it some how made it work. Of course he said it made the carb's idle really rich. He never said anything further on the issue.

I'd love to get my hands on an actual Sterling to correct all of its faults. Oh I doubt there's any secrets I'm going to stumble on and then not share with the forum. These carbs are so simple that I can usually tell what's been done to it just by looking at pictures. But I will share whatever I find. Why wouldn't I? He's not in business anymore. And I think my carbs are better anyway.

This is healthy. I feel all this needs to be said. It's the only way we will move on as a forum. If you guys think I'm Sterling bashing, you need to go back and reread this post and the one above it more carefully. If I was actually bashing Sterling, I'd come right out and say it. I'd say far worse things than simply mentioning his strange manic-depressive behavior in his posting style and how he took on too heavy a work load and then would come on the forum to complain about it, as if that's supposed to satisfy his customers or something. Customers who spent like 400 bucks and then never received a carb. Who does that? Or before he stopped delivering carbs, he'd make you wait 6 to 8 months as I recall. And the carb that would show up wouldn't even idle, or it would flood because he would swap out the nice OEM needles and seats to swap in the garbage parts included in all rebuild kits. Or how he would paint carbs to make them look "better". And how he would mix up parts (air horns, main bodies, base plates) and think that was why his carbs didn't want to idle. Um, I've swapped all three of these parts on my carbs to test this theory and it doesn't affect the idle at all, unless the bushings in the throttle shaft holes were a bit worn, but that only affects a freshly rebuilt carb where there isn't any oily crud buildup, and it's only a slightly unsmooth idle, which is still an idle. And a little driving makes this problem go away. They get nice and smooth after a little driving time.

I certainly do not thin my throttle shafts because as you know it weakens a part that needs to stay sturdy for boost. I like a reliable part that I know will perform whether I lightly floor it, or I mash the pedal. I also know it will consistently work in all temperatures because as you might know, when things heat up and parts expand, the distance the throttle cable must travel to fully floor the carb will change and cause the pedal stop Yaw and Sterling carbs require, to either not open the throttle all the way, or tend to open it further than intended due to the adjustment having been set on a cold engine. Then you end up with a bad idle because one butterfly is open more than the other thanks to a twisted throttle shaft.

See, it's little things like that, that folks like Sterling, who seem to need to reinvent the wheel because they can do it better than Mazda, always falter on. But I can tell you exactly why Sterling's carbs didn't want to idle. Aside from any other actual physical problems that I don't know about such as a possible twisted shaft or just a misaligned butterfly or whatever, but knowing these carbs as I do, I can venture an educated guess. Ready for the actual secret? Primary short slow air bleeds.

Make them around 118 and your carb will always want to idle, assuming everything else is good.

I'm not bashing Sterling. I am complaining, but not bashing. Now I suppose some of his devoted customers will say I don't have a leg to stand on because I never got shafted by him, never sent him any money or any carbs. To that I say, thank goodness! Glad I never had to deal with him on that kind of level. They say doctors make the worst patients. Because I'm technically minded and had the propensity to do this carb work myself, and the fact I'm not easily swayed by strong personalities, I never got around to sending a carb to Sterling. Even though Sterling said he'd place any carb I sent him at the top of his list (what the?) I simply never got around to it. Oh, I know why. I couldn't justify 400 bucks on a carb that was meant for a 12A when I had a 13B. See? But I was also pretty ignorant myself back then. These days I'm convinced the Nikki can do anything. It is the best carb for a rotary period (with side ports, not peripheral of course). When all you have to choose from are:

RB Holley
off the shelf Holley
Edelbrock
Weber IDA, DCOE, IDF, dual DCD
Dellorto
Hitachi

And we know of the problems each carb has:

RB Holley carbs have issues with flooding in corners, even with center hung floats. You also have the poor workmanship. Compare it with the excellent fit and finish of a Nikki and you'll see what I mean. And then when wankel=awesome said his personally hogged out Nikki was better than his RB Holley 465, a Nikki he modded following my instructions I freely posted on the forum for all to see, compared with the RB recommended 465, I felt vindicated.

Off the shelf Holleys, as we all know, were designed for open plenum intake manifolds found on V8s, not the separate runner manifolds RB sells. There have been attempts to make these work using a 4 hole spacer with a channel cut to connect both primaries together. I did this with some success on an Edelbrock on an RB manifold, on a 6 port. It worked but I wouldn't do it again.

Why did RB insist on separate runner intake manifolds in the first place? I think it had something to do with when they were designed and the OEM intake manifolds widely available at the time. I'm talking about old school REPU and RX-2/early RX-3 intake manifolds that had separate runners. RB's Jim Mederer and crew wanted to use the widely available Holley because no one knew how to mod the Nikki back then, or realized it would be more work than extensively modifying off the shelf Holleys. Um, what? If they both require mods... oh wait, I get it. RB's carbs are drilled here and there to accept the strong reversion pulses and don't require the much more extensive modifications I do to a Nikki, which in the end, according to wankel=awesome, makes the Nikki a more powerful and more driveable carb. Oh and I'm sure back in the day, RB's carbs were not as expensive as they are now. Back then, Holleys were still found on new cars so it kind of made sense. These days, with the internet and much higher prices, you're better off sticking with the Nikki. A 100,000 mile Nikki with a rebuild kit and a hogging out plus other mods the way I do them, will run better than a new Holley. lol

Already mentioned Edelbrock but I'll say this about the few I've tried. They always have a stumble when you slow down and turn left. They go pig rich and stall. They become an unpleasant carb to drive. Whether it's on a supercharger or just on an RB manifold as mentioned above, it's the same behavior. However I will say their cold drivability is actually quite nice. Electric choke and easy to get to AF mixture screws. Also a plunger style accel pump make for a nicer carb than a Holley. But that stumble...

I don't know much about webers but I do know they were designed for a lazy 4cyl where each piston got its own barrel which, when used on a rotary, requires these carbs to idle on the first progression hole. They also require you to drill out your idle jets to 120. And then if you try to use a turbo with these, the extremely wide dynamic range of a rotary with boost doesn't translate well to a 2bbl carb. This is why, off the top of my head, I can mention some names of users of this forum you may recognize, who tried the boosted Weber, and had to give up because it sucks. That would be IoTus, hyper4mance2k and PercentSevenC. These guys get fed up with the poor... everything about these carbs and switched back to NA or went to fuel infection. This was of course years ago before I figured out what needed to be done to make the Nikki work great with boost. Basically all the problems the webers have that can't be solved, were solved with the Nikki.

What else? Dellorto. I know even less about these but I did have access to one once. It had better grunt than a stock Hitachi, which isn't saying much. Can you boost them? Don't know. All I do know is RB did some testing back in the day and discovered that on a GSL-SE that made 135HP stock with ancient OEM EFI, they first swapped their long primary exhaust in, which increased power by 21HP to 156, then swapped to the Dellorto which increased power another 21HP to 177. Not bad. But I doubt it was enough to break it loose in gear on dry road. I say this only because I have not dynoed my setup yet, but I think it's making at least 160 real HP. It can even break them loose in 3rd gear which I know is a lot more difficult than in 1st gear, so something doesn't add up here. Either my tires are so slick that they break loose if you just look at them sideways, which probably isn't the case as I can drive just fine when it's wet out, and they have plenty of tread left, or someone's numbers sound a little artificially inflated. Or maybe I'm making closer to 200HP? I guess I'll never know until I get it dynoed. But then I've had people tell me they love the torque my setup makes. Who knows.

Lastly the Hitachi carb, OEM on all 13Bs from the 70s and some J-spec cars from the 80s. These were nice with slightly better driveability on the slightly bigger 13B using a plunger style accel pump that felt like it had decent tip-in. Just not a lot of power. They always left me wanting. The later carbs coming with the smaller 20mm venturis and increasing emissions controls mounted all over the carb like all later Nikkis had made things even worse. Only the early ones had 22mm venturis. Wow, 22mm!?! Isn't that like a Sterling? Isn't that a much more powerful carb to drive than any stock Nikki and any 20mm hitachi? No, not really. The actual differences were small and hardly noticed. Yet back in the day, the 22mm Hitachi, or so called RX-4 and REPU carbs were the shiznit. Highly sought after. If you could plunk one of these babies on your RX-3, you could easily take out V8s! A bit before my time, but I don't doubt it. The only car I have that even comes close to a 3 is the GLC. Same engine bay, anyway. And yes I tried my genuine 22mm REPU Hitachi in it, 13B of course, and yes after I got the secondaries working, it was a fairly amazing experience, but I've since had far more performance from hogged out Nikkis in the brown car and plan on throwing one of them in the GLC. I probably won't even need a turbo at that point. The NA tuned hogged out Nikki will walk all over anything the Hitachi could have produced and do it much better than an RB Holley, which by the way I also tested in this car. Speaking of which I also tested a Camden 5" and even the 20B! The only carb that ever wowed me was the RB Holley. Yes I know the 20B should have, but it simply didn't. Neither did the Camden believe it or not. Only the Holley gave it the wow factor the car had been lacking. And now that I know what I'm doing with Nikkis, I feel the wow factor will be available in even greater doses. And when it gets boring, I can always add a turbo like the Aussies and Kiwis do.

I'm am convinced the Nikki is the only carb choice we should make these days. And if you must have a p-port, do it the j9fd3s way. Or go EFI and avoid one headache by creating another one for yourself. lol

So go on and say I bashed Sterling if it makes you feel better. Just know the truth that I am not bashing Sterling. It's because I have no need to, because he never stole money or a carb from me. If he had, this post would have been different. All I'm doing here is exposing things based on the way I understand them, and that's all anyone in my position can do. I like working on these carbs these days. I stopped feeling like I was going Ster-crazy once I streamlined the process. I do custom parts in production runs from accel pump extension pieces to hogged out venturis and even blue thick baseplate gaskets. I did 14 from the nice long roll Erick sent the other day. Man, that was a lot of cutting!

If I'm going to bash anyone, it would need to be that SVT guy. He butchered carbs. His carbs didn't run at all. I had to spend more time undoing all the damage he did on Jingkun's carb than it would have taken me to simply tear down, clean up, and hog out/modify a pristine stock carb. Jingkun's carb was a trainwreck. It used up so many spare parts from my mini carb spare parts pile that I honestly can't take on any more of these basket cases until my parts stash builds up some. There was one other customer of that SVT guy who recently made a post about it, and I tried to help as much as I could, but there is only so much you can do. Hopefully he gets it sorted out.

I now have a set of venturis cut by that SVT guy, which I swapped out of someone's carb recently. The most off-base misguided attempt at a venturi cut I've ever seen. The narrowest part is 9mm below the bottom of the booster. The little hole in the venturi lines up with the bottom of the booster and is used for vacuum secondaries. I use this as kind of a land mark. Ideally the little hole should be at the narrowest part, they way the factory had it, but I have not found any issues so far with the narrowest part being above the hole. I hog my venturis from the bottom up. The SVT guy hogged his from the top down. The results are his get cut out to 22mm and the narrowest part is 9mm below the hole. Mine get cut to 24mm or 25mm (depending on the application) which is a few mm above the hole (I'd have to go and check the actual distance but I know it's a lot less than 9mm!). The result is his venturis simply don't develop enough vacuum to run. Mine develop plenty and run great!

I'm not actually bashing the SVT guy either. For one thing he is also gone and can't defend himself. But if he was here, he'd have a whole bunch of angry customers wanting their money back to deal with. I never sent money or carbs to him so I have nothing against him personally other than to say he didn't know what he was doing and should have known better than to ruin a bunch of people's carbs and then get paid for it. Did he not even test drive any of the carbs he ruined? My guess is no because his carbs didn't even run. At least Sterling's did, as I've been told, even though they didn't idle and he didn't test run them either. I'll never understand.

Wow, another long one.
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Old 09-06-15, 12:41 PM
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A quick show of hands: Who still drives a Sterling carb? Who drives a Yaw carb? Who drives (yeah right) an SVT carb? Who drives a carb or carbs they modified themselves?

I know of one guy who drives a carb he modified himself t_g_farrel. Anyone else?

Last edited by Jeff20B; 09-06-15 at 01:17 PM.
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Old 09-06-15, 01:09 PM
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Nice write up Jeff, thanks! Lots and lots of helpful information.

I've only used stock Nikki's, but the next one will be a hogged Farrel because I'm going to get him to help me do it.
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Old 09-06-15, 01:23 PM
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I suppose a Farrel carb will work just as nicely for you as it did for him, but just know he kinda simply hogged his out without really knowing how big to go or what he was doing. I, on the other hand, have done enough of these carbs now that I've gotten most aspects down to a science. The rest is nearly there. Such as how far to bend the accel pump extension pieces. Little things like that. But the big important stuff is all there now.

Let us know how the carb works out for you!

Hmm, I'm curious. What time frame are you looking at? I tend to get a carb done in a week. Sometimes two weeks if I'm busy.
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Old 09-06-15, 01:33 PM
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Thanks for the wright up, lots of good info. Hope you had a beer after typing all that. :-)

I like the idea of using a carb for a dayling an old car, over using efi.

However, i can always respect a properly setup and tuned carb setup on a boosted application.
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Old 09-06-15, 03:25 PM
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Originally Posted by Jeff20B View Post
A quick show of hands: Who still drives a Sterling carb? Who drives a Yaw carb? Who drives (yeah right) an SVT carb? Who drives a carb or carbs they modified themselves? I know of one guy who drives a carb he modified himself t_g_farrel. Anyone else?
Me. I had a sterling, I like mine better. Less power, more useful.
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Old 09-06-15, 04:09 PM
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I hear you Jeff, you West Coast guys are big thinkers. Breathing pure air is a major priority out there.

But me, I just need a nice fast Nikki to run my moonshine. From what I hear those Farrel Nikki's eat up those mountain roads.

Like he said, less power, more useful.

Of course once you make it to the mountain top, you always want to find a taller mountain.

So again Jeff, thanks for posting this, I'll be looking it up in a couple years.
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Old 09-07-15, 07:19 AM
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Hopefully this thread can put the sterling worship to an end. Unfortunately I know he owes a lot of people money. Nevertheless, the carb he would have sent you wasn't really correct. They were good, but not great. I had one of his first modded nikkis and as jeff described the mixture screw was useless. I could turn it all the way in either direction with no change in the quality of my idle. It also got absolutely wretched fuel mileage. It did start up every time, idle pretty good, and made some noise when you punched the pedal. It bogged off the line pretty bad always, and would choke itself out on hard left hand turns. All as jeff described abobe.

I was wet behind the ears then so i didn't know much about carbs, and sterling was really starting to ascend his rx7club pedestal, mostly of his own doing. I mentioned to him that I thought it was running really rich and he pretty much dismissed my claims as there was no way i could be right according to his calculations and theory. My calculations said i was getting 8-11 mpg on a stockport 12A with rb exhaust, taurus fan, ignition upgrades, and a K&N filter. I couldn't understand how others on the forum were getting mpgs in the 20s. Now i can.

Sterling carried us through the gap between Yaw and Jeff. He got us thinking and testing and trying to copy what was no longer available. Maybe that was his greatest contribution. He left us all ticked off and wanting what we couldn't have, a modded nikki. What Jeff has posted above is what dennis aka sterling couldn't get his head around. How to make these carbs versatile, boosted if desired, idle right, turn left, and break them loose off the line despite mech secondaries. As far as im concerned Jeff has started the renaissance period for nikki carbs. This is within your grasp people. And it requires far less modification than we used to think.

I think the lessons to be learned here are:

1)Dont steal $300 from half of the forum members.

2) Dont do all your thinking on the notepad and computer and workbench. Get some real world data.

3)Listen to Jeff. He knows what he is talking about and then some.

Just wanted to share my observations from the past 10 years ive spent here.

Jamie
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Old 09-07-15, 07:58 AM
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Lots of great information here. Should be archived.
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Old 09-07-15, 12:02 PM
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Wow, thanks Jamie. A pleasant thing to wake up to today.

It's hard for me to see the forest for the trees, as it were, being in the thick of it. But you summed it up perfectly.

I appreciate that you brought attention to the Sterling worship. If you go back and read any carb thread from ten or more years ago, you see it constantly. Kind of sickening.

Probably the worst thread was from late '04 where a young enthusiastic but very noobish guy got the first ever boost prepped Sterling/Carl Nikki. This was a big event for everyone involved in the subject back then. Kinda makes me wonder where it all went. Social media probably. It's probably for the best as when I read any of it now, they all seemed to be high on something. It doesn't start getting interesting until post #81 where he says it won't rev past 3000 rpm. https://www.rx7club.com/1st-generati...4/#post3289056

Anyway after reading page after page and getting a headache and feeling increasingly frustrated at the slow motion trainwreck I see before me, I'm practically yelling answers at my monitor (but knowing full well I'm about ten years too late), the poor guy had to give up and go with a Robert at RotaryShack carb.

Man, it's crap like that thread that make me really appreciate all the knowledge we have these days. Practically anyone can have success with a hogged out boost prepped Nikki now because we've figured out all the kinks. And we don't require personality worship to get there.

I'm going to put this new personality-cult-free information to a test soon. I've got two turbo setups coming up. Baja and Icy. Gonna get started building the Icy engine pretty soon. I'll keep its build thread updated for you guys.

Speaking of which, I just got another carb up and working yesterday. On this one I decided I'd aim for slightly smaller venturis than I had been doing. This was back in June when I hogged them out, to only 24.45mm. Why so small? As an experiment just to see how they'd turn out. It's right before I did Jingkun's venturis to 22.3mm after he requested a Sterlingish size of 22mm. As it turned out, 22mm is a bit small for my 13B however its driveability was exceptional - just lacked a little transient response is all. Its high RPM was great too, just not as powerful as my larger hogged out carbs, as expected. So I was glad I decided on a slightly bigger, but smaller, for me, size of only 24.4ish for the baja, which has a stock port 13B with Y irons.

So I finally had a little time to finish this carb and test drive it over the weekend. Oh by the way, see where I'm going with this? Field testing! Oh boy! Yes, you simply must do this if you're dealing with a device such as a carb. You have to test it on a running engine; an engine you know well and have enough instrumentation such as a fuel pressure gauge, boost gauge (if boosted), wideband (a must!) and then any other gauge you like to have around. The carb has to have fuel going through it to test the idle circuit and adjust it so it runs best for your engine. You can't just guess. Mine liked 12.2 on the wideband the very first time I ever hooked a wideband up to it, so that is where I tend to aim for with every carb. Of course back then it was still a fresh rebuild and needed a slightly rich idle. These days it is fine with 13.2 but that makes it harder to keep running when its cold. And I've kinda gotten used to looking for 12.2 on the wideband, so when I see 11.8 which then creeps back to 12.1 or 12.3 and fluctuates around 12.2, which it does, I know the engine is happy.

Anyway enough about that. I just thought it might be helpful to anyone who's thought about getting a wideband but hasn't yet. Oh and I've been told my 12.2 setting worked great for a guy who got a basic stock rebuild from me last year (he's on the forum and used to own the red vert FB you might have seen in the "my post pictures" across the top of the main page today). He said it ran perfectly for him right out of the box. This carb wasn't boost prepped at all, and still had the stock choke flap, vacuum secondaries etc. Didn't stop me from testing it on my turbo setup. It actually ran great! I don't recall whether it needed to be fine tuned, but I do know it had stock 92 and 160 jets along with stock 70 and 140 air bleeds. I only upgraded his primary short slow bleeds but now I don't recall what size I put in. Either SA 150s or smaller such as 118. Oh well. Either way it ran perfectly for him.

Don't get confused about idle tuning. Don't try to aim for some number on a gauge. Instead, do like j9fd3s says and give it what it wants. Mine just happened to want 12.2.

Getting back to the 24.45mm carb, its accel pump needs a small adjustment and the throttle shaft bushings need a little wetting from oil, which will build up over time. Otherwise this carb is nearly perfect! Oh the OMP linkage squeaked so I'll lube it up a little today.

How was the power? Pretty good actually. I could accelerate normally through the first three gears just getting up to the speed limit like we all do, in primaries only, and it responds well with decent tip-in. At other times I'd go through first gear normally, not really pushing it, then in second gear I'd let the RPM climb to 3000 then punch it. The result was instant perfectly opening secondaries with zero delay and the *** end scoots a little sideways very smoothly. Then I let off and shifted into third while the BOV is making its sound we all know and love, and the carb goes back to a low RPM primary mode without a hint of flooding. It took me over a year to solve the flooding after you let off from a short flooring episode, and the secondary delay, once you actually drive it the way a mechanical secondary carb should be driven, has been solved through air bleed tuning. And even if you floor it too early or too late, it doesn't complain like a Sterling would. Again, air bleed tuning.

I didn't bother to tune the fuel jets much beyond a basic whatever tune, because I'll worry about that once it's in its intended vehicle, but the part throttle cruise ended up around 13.0 so I'm happy with it. I couldn't look at the wideband when the secondaries opened because the car just goes sideways. I need a passenger to help weigh the car down lol. But I think it has 146 secondaries. The primaries are 114.

My clutch is slipping now. Yep, I'm making enough power that a new disc with only about 150 miles on it is slipping in 2nd gear. I think my pressure plate is a stock duty so I'll look around for a street strip. The disc is one of those ACT modified street discs with the limited marcel and the copper woven into the friction material for heat dissipation. I didn't think it would do this so soon because I thought the pressure plate was one of those old school red RB SS jobs. But then the pedal wasn't as stiff as when the centerforce was in there. Which, by the way, never slipped even after 325 miles. Oh well, I'll pull the disc at some point and see how thick the material still is.

The next carb to get up and running is a 25.15mm. I wonder if I'll like this size the best. Doesn't seem to big or too small. But I'm not going to say something dumb like Sterling might have at this point, calling it a goldilocks carb or something idiotic like that. But I hope it's just right.

Last edited by Jeff20B; 09-07-15 at 12:16 PM.
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Old 09-07-15, 01:38 PM
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Ok guys, I want you to read something. It's in that trainwreck of a thread I linked to above. https://www.rx7club.com/1st-generati...6/#post3301022 It's post #147 where coldy13b spills the beans about the jetting of a Robert at RS carb, in reference to a post by Sterling he quoted. He said "adequate jetting" was the same size as stock jets. Bigger jets caused a huge bog/stumble when first getting on boost.

I'm like holy crap! Yes! This is exactly the information I was wondering about regarding Robert's boost prepped carbs. If it is to be taken at face value, this proves that Robert did not hog out his venturis or change his air bleeds! Because if you leave the venturis at their stock 20mm size and leave the air bleeds stock, there is no need to increase jets, because if you do, it makes the carb run way too rich. You only should increase your jet sizes to match an increase of air from enlarged venturis. That's it. Pretty simple, really.

But the thing I want everyone to pay attention to is how this adds weight to one of my suspicions about NA tuning that I haven't been able to prove ever since the turbo went in. I've suspected for a while now that an NA tune wants the same or very nearly the same size jets and air bleeds that a turbo tune would want. I just can't prove it in my own vehicle so I've been recommending a range of jets from jetsrus to anyone who asks because I can't give them a definite answer.

But the idea that keeps running in the back of my mind has to do with how a turbo is simply a way to artificially increase the atmospheric pressure above and inside a carb, but the carb still has to run a certain way under vacuum which is very similar to an NA tune. I keep aiming for a 13.0 part throttle cruise which is obviously when the carb is in vacuum, like when it's NA. So it's my understanding that this vacuum "mode", even with a carb hat and a giant cork in the exhaust system (turbo), is almost equally translatable to an NA setup with a free flowing air filter and a long primary exhaust. Obviously a little fine tuning will be required for the freer breathing of an NA, but nothing drastic.

Maybe I just don't have the words for it today so I'll cut to the chase, as they say. What coldy13b said proves to me that a Robert carb is simply a very lightly modified stripped Nikki that has stock venturis, stock jetting, stock air bleeds, mechanical secondaries and the associated problems that he never corrected, and a removed choke flap. His carbs were known to have a secondary "hiccup" as his customers were known to say often, and it was due to the probably less than adequate accel pump duration, and a lack of air bleed tuning. That is why I always do the Sterling accel pump mod on every carb. No exceptions. Even for NA, because I also always do mechanical secondaries. This requires tack welding the sec linkage in this one spot that is easier to get to when the carb is apart.

It's just amazing that the differences between NA and boost are a lot smaller than I think any of us had considered before.

Wow!

I too experienced the huge bog/stumble caused by jets that were too large, just as coldy13b described, last year when my air bleeds were stock. I tried a set of jets drilled out to 208 because I didn't have my micro drillbits yet, and 208 was the next step up from 160 and 118 which are all actually SAE sizes I had. The result was a bog that lasted longer than any I had previous experienced. We're talking 3 seconds at which point I let off and that was it. Pulled those suckers and never tried them again.

So there you have it. Robert at RotaryShack boost prepped carbs are barely modified stock Nikkis with a few necessary/obvious upgrades but nothing amazing or noteworthy. Glad I found this out today. I wonder how much he charged for them?

I'm not bashing Robert at all. I simply know now that my carbs are way better. Tee hee.

It goes, in order, something like this: Yaw, Sterling, ME. Each time we add something new and profound to the Nikki and try to clean up the previous guy's approach. There are others like SVT and Robert who I won't get into here. Then you have the individuals like bad_83 and others who mod their own carbs. Glazeham42, t_g_farrel, Oneiros, LizardFC, Qingdao etc.

According to Sterling (in a post of his from years ago I read part of earlier today), Yaw carbs had less mods than a Sterling, and the quality of the metal work was subpar. Such as for the boosters. They look ugly as I understand it. Probably not as good for airflow as a properly airfoil-modded set from Sterling. It was just enough to get the basic job done for racing. And that was all they were intended for. To be legal for various racing classes. If you happened to drive one on the street, it was more powerful than a stock Nikki. And more tuneable, to some extent. But they all had the crappy holley dominator air bleeds as fuel jets and didn't have the Sterling accel pump mod so you'd get a secondary bog, and some didn't even have mechanical secondaries as you can see the vacuum box in pics of Yaw carbs. Or maybe it was just disconnected at the linkage but the housing was still there. He and Sterling also had an allen head screw fetish which I'll never understand. The stock screws work fine, guys.

Sterling carbs took a Yaw carb to another level. In some way better; in some ways worse. At least All Yaw carbs always worked as far as I know. I think Sterling started chasing the unicorn horn of ever increasing CFM, as if that was the holy grail of the ultimate Nikki or something. As cookboy said, his carb had less power, but was more useful.

Of course myself. But I'm not running a business or anything like that. It's just a hobby that one does on the side when free time is available. I just like to spill secrets all over the forum, so you end up reading a lot about it.

SVT was a backslide. Did more harm than good. Best left as a lesson learned.

Robert carbs, as mentioned above, were lightly modified just enough to handle boost and that is all. Nothing special. Of course I'd love to get my hands on one of his carbs or maybe a customer of his could post up some pics of the internals? No need to be so secretive in this internet age. Maybe some of my info can fix your Robert carb?

Then we have all the individuals modding their carbs in various ways. I'm curious to see how they turn out, like the next fat Nikki from t_g_farrel for Ray.
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Old 09-07-15, 04:31 PM
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Originally Posted by Jeff20B View Post
It's just amazing that the differences between NA and boost are a lot smaller than I think any of us had considered before.

Wow!
the short answer, is that yes, airflow is airflow, so 170hp NA and 170hp turbo aren't any different as far as the carb is concerned.

the long answer is that after doing a bunch of turbo cars, i've done a bunch of NA cars, and i'm really happy i did, especially the P port, as it really made me tune it. the P port is actually the easiest of the bunch to tune in a way, as the AFR range where its happy is a lot smaller than the stock port engines. too rich? you get angry fire spitting beast. too lean? it doesn't run. but get it right, and it turns out to be a happy little guy. mine is like a labrador, it just wants to run after stuff.

the best thing that happened was that i had to ditch the jetting chart, and go through the carb piece by piece, and try a bunch of AFRs, and see what the engine liked. i learned a LOT. (ive played with a few piston cars too)

whats it all mean basil? well hp is airflow, and so as far as the carb is concerned it just needs to meter the right amount of fuel, per the right amount of air. simple!

well there are a couple gotchas, the turbo usually makes its airflow at a lower engine RPM, so chamber pressure is higher, and the turbo air is hotter too, and with both we need to be more careful about detonation, but there is no magic in it, it just wants less timing, a richer mixture and maybe colder spark plugs. the higher you run the boost the more hp you make, so the more the little stuff matters.
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Old 09-08-15, 06:11 AM
  #14  
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I literally copied Jeff20B's nikki car tuning and machining for NA and it came out perfectly.

I made a few changes to mine as far as jetting, but ended up going back to about where he suggested.

Mine has 24.5mm primary chokes, 26mm secondary chokes, 11* inlet angles, 7* outlets.

I also did all the tricks to improve airflow, and converted it to mechanical secondary.

Ended up with 115 main primary jets and 160 secondary jets. I dont remember the air bleed sizing completely, but I know my slow bleeds where 118 pri slow and 60 secondary slow.

It worked nearly perfectly on the engine the first time. Very simple and a full range of tuning for the idle.

Only thing that would make my FB more fun is a lightweight flywheel...
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Old 09-08-15, 08:15 AM
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Wow! Nice brain dump here Jeff. Finished the first post and skimmed the second and others. I'll have
to come back and reread later when I have more time.

Yes, I hogged out my own nikki. Yes I was a noob at it. Yes a learned a ton from it. Yes Jeff and I
had some conversations along the way which were always useful.

I like to think that my way of hogging the nikki out was more intuitive. I read and collected up all
the mods I thought made sense and did them. Do I know how much bigger the venturis are? No
clue but they are shaped nice still and seem to work really well. Someday I'll get an accurate
gauge and measure them just for fun.

Ray if you send me a nikki don't expect it done for at least a few months. After, all my own took
me 2 years
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Old 09-08-15, 10:26 AM
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I have to confess, I'm pretty good with mechanical thinks and Nikki's in particular, but every time I try to read and understand one of the excellent carb posts that Jeff, Tim and Jamie have contributed in recent years, I get lost on the second paragraph.

So Tim I'll have a Nikki in the mail for you this week. I've got a couple I recently rebuilt on the shelf, I think I'll pull one of those so it will be nice and clean, with fresh gaskets and seals.

I'll include a second complete unit for your parts supply and I have several others in various states of repair if needed.

Then we can compare notes with Jeff and, with a little luck down the road, compare carbs side by side.

And when these things pass Quality Control, we can start a business, Hogged Nikki's Ltd, or something like that. I'll be the manager, you guys build the carbs. Once we've sold a few we can go on Shark Tank.

It's all good!
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Old 09-08-15, 12:00 PM
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Yay, people are responding to this "brain dump" thread I created. I kinda figured I'm at a position now where I might as well dump it all out there before I forget anything over the winter.

Ok I have a couple of corrections to make. It turns out Sterling wanted $300 for his carbs, not $400 as previously thought. I think that SVT guy also first asked for $400 then reduced it to $300. In my opinion, $300 sounds reasonable for the amount of work that goes into these.

I also should point out something about where I mentioned the differences between NA and boost are a lot closer than we thought. What I was getting at is when a carb has been fully boost prepped, such as when it has all the secondary air bleed mods, this configuration is 100% compatible with NA. It's just that when you reduce the air bleeds this much compared with stock's wide open configuration, it requires you to reduce the secondary fuel jet size from its stock 160 down to... most likely 140, 145 or 150. Otherwise when you open the secondaries, you'll see a pig-rich condition on the wideband. They kick in fast and hard, but super rich. I've seen it myself with my turbo. I just don't have any recent NA driving time to test my boost prepped modded secondaries.

The actual differences between OEM stock vs what I discovered that works great on my setup is this:

OEM NA:
140 main w/ emulsion tube
fully open sec long slows
nickel plated 60 short slows
160 fuel jets

My turbo modded secondaries:
modified 80 main w/ emulsion tube
fully solder filled sec long slows
swapped in solder filled brass primary short slows drilled to .37mm or so
140 or 145 jets

Even though my secondary venturis themselves are stock, the reduction in air through the air bleed circuit requires me to use smaller fuel jets. It's not about boost vs NA, it's about finding the right size jet to give the right AFR on the wideband. I just happened to discover that my engine wanted 140 to 145. I tried a set of OEM 150s which are actually closer to about 148 (remember the three number rule when dealing with factory drilled jets is usually two or three numbers smaller than what they stamped on it). With the factory OEM 150s, it started off too rich at 10.0, but then leaned out perfectly to 11.5 and held there as long as I kept it floored.

This was a little strange as I had not seen that particular behavior before. It might just have been that one particular carb acting this way because previous carbs were fine with 140 jets. It also might have been some premixed fuel I was forced to use for a little while to test a carb that had its OMP nipples deleted by the owner.

As you can guess, premix oil displaces some fuel and creates a leaner condition, but by how much, I have no idea. It must depend on the ratio. And it might vary because the oil is not "premixed" before it enters the tank. It is supposedly mixed after you dump it into the tank first, then fill the tank with gas. How well does it actually mix? I honestly couldn't tell you.

I do not recommend doing this because it's hard to get the premix ratio right every time. And it's been said the OMP works fine up to 10psi. Of course I can't prove this information. It's just what I read on the forum. I'm running at probably about 9psi now with a manual boost controller on a stock S5 turbo with a full 3" exhaust which does spike to at least 7psi up from its factory 5.5psi wastegate spring, because the factory wastegate holes are small and designed for a 2.5" exhaust. Note the stock S5 T2 made 9psi but it was due to an ECU controlled solenoid, not the wastegate spring. But enough about that. What I can do is I can just pass this info on about the OMP and recommend to keep it. Don't delete it - it's more work and the carb becomes less usable. If you want to premix, that's fine, but watch the ratio and keep the OMP. Oh, I also read somewhere else on the forum that premix reduces octane. I always get 92 which is the highest pumpgas in my area. Works fine with 10 degrees semi-locked dizzy and S4 NA rotors.

So getting back to what I was talking about regarding secondary jet sizes, if you have an NA carb with no aspirations for boost, I can recommend keeping all the secondary air bleeds and the factory 160 jets if you want to, like wankel=awesome and Jamie. However you need to understand that the mechanical secondaries require the Sterling accel pump mod because without it, there will always be a short bog when they open. You also run the risk of a bog if you open them too early like cookboy was experiencing. By too early, he said 4000 which in my opinion is too late! I don't know wankel=awesome's situation about where and when in the RPM range he can open his and not experience a bog, all I know is when I do my boost prepped secondary air bleeds and the resultant smaller fuel jets, I don't get a bog at low RPM and only get a slight delay of 1/8 second up to maybe a 1/4 second max at high RPM. We're talking at 6k. So at this time I can still recommend my secondary boost prepped air bleeds, even for NA use, but it is more involved and requires some micro drillbits and a couple spare sets of jets, one of them being pilot jets which you can drill out to 80 for the mains, and the other jets will need to be a set of spare factory 92s (with their deep funnel shape for high RPM use, which you can't get from jetsrus) drilled out to 140 and then go progressively bigger until your ideal AF mixture is reached. It's NA so you won't hurt it if slightly too lean. Just don't keep your foot in it if the wideband is showing that it's too lean because it heats up the engine. What is ideal for NA? Isn't that like 12.5 or something? All I know is a boost tune wants 11.5. Wankel=awesome? What is your carb's secondary AFR with all your stock air bleeds and jets?

By the way, on my latest carb with 24.45 primary venturis, I have 70 air bleeds and 114 jets. Perfect 13.0. Of course 118 drilled primary short slow bleeds. I seem to recall your primary air bleeds were 70s which I recommended you swap in because your carb's factory 90s are just too big and reduce tip-in (they also don't work with boost, heh).

Because our tunes are perfect and the sizes of things are 99.9% the same, is it safe to say that a boost tune and an NA tune on the primaries is identical? Can we wrap this one up?

Makes me wonder about the secondaries. Can a boost tune and an NA tune also be identical? It makes sense. j9fd3s seems to think so. Anyone care to test it and tell me your AFR? Do I need to ship a set of modded sec air bleeds to someone? Seems like less work than having to pull all my turbo parts to swap the RB long primary exhaust back in.

Oh wait, I recall wankel=awesome said he filled his sec main bleeds with epoxy and drilled them to a smaller size. I don't recall what size. They were a set of unusable 160s. That's WAY too much air! What was the factory thinking? So since your main air bleeds are in fact probably smaller than 140, hmm...

Ray, you could send a carb to me. I take about a week to do all the mods. Maybe two weeks if I'm busy on other stuff. Then you guys could tear it down and look at all the mods I do. Doesn't bother me at all. Just get it back together right so it runs.

If you decide to send me one, please make it a factory carb with OEM needles and seats and totally stock floats. If I find they've been tampered with, I'll throw one of my tops on it to do the test running/driving because I don't want to risk flooding my engine out with aftermarket seats. Been there, done that, fouled my spark plugs pretty good.
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Old 09-08-15, 12:59 PM
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Originally Posted by Jeff20B View Post
Makes me wonder about the secondaries. Can a boost tune and an NA tune also be identical? It makes sense. j9fd3s seems to think so. Anyone care to test it and tell me your AFR?
they could, but i think it is better to assume the turbo will need to be richer, and thus different.

we've spent a lot of time on the dyno this year*, and just generally on gasoline an engine will make best power in the 12.8-13.2AFR area, not really news, however the power difference between 12.8 and 13.2 is teeny. furthermore if you're using a butt dyno, or a stopwatch; both or which are valid, i really doubt that anything leaner than 12.5 is noticeable.

given that we, aren't racing, and we do want a little safety margin, it is better to be a little rich than a little lean. we even tune the race cars to high 12's, as even piston engines need a safety margin**.

with a turbo engine, you have higher intake temps, and if its making more torque at a lower rpm, you have higher combustion pressures. both of these require a richer mixture, as a richer mixture is less prone to detonation, factory turbo cars run very rich, the FD is in the high 10's and the mitsubishi evo's are in the 9's. since the turbo is making its power by more airflow, its best to just run it rich and if more power is needed, bigger turbo, more boost, etc.

the actual AFR with a turbo depends on the turbo, gasoline, and how much boost (power), but 10psi, on pump you should be mid 11's. (you would also want less timing)

if the carb does both with the same jets, it would be unexpected, but i've seen weirder.

*ironically our class limits us to 136hp and 2336lbs, and it makes 147, so we spent a lot of time trying to make LESS power... adding fuel and pulling up to 6 degrees of timing is like 4hp, so we had to buy a restrictor.
**we've all read about rotaries that are fine one day and then pop the next, piston engines will do it too, been there done that, have the shirt.
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Old 09-08-15, 01:53 PM
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Thanks for the info, j9fd3s.

Last year while NA testing, I discovered an NA tune actually wanted a richer mixture than a turbo tune. But that was with limited knowledge and the wrong parts. The carb had 90 primary air bleeds and all stock secondary air bleeds. Obviously with these large air bleeds, it needed a lot of fuel to compensate. Of course its secondary delay was 1.5 to 2 seconds and you may recall I was getting pretty frustrated with it.

But what was weird about it was when I installed a carb with a turbo tune onto an NA setup, it ran extremely lean. I then discovered swapping from 90s to 60s helped a lot but caused the slight glitches all 60s seem to cause when combined with enlarged primaries. But it fattened up the primary tune on the narrowband!

If I had it to do over, I'd have gone with 70 air bleeds right from the start and tried a jet size slightly larger than whatever it had at the time. Probably 118 because that was the only small dirllbit I had last year. I did test a set of factory 130s (about 127 metric) which worked a lot better in a different carb with about the same size primary venturis, NA. When I tested this carb with boost, it was fine with the 118s.

So this is where the idea that an NA tune wants to be richer came from. It came from having the wrong size primary air bleeds which was based on some bad info on the forum where a guy recommended buying a 1mm drill bit and drilling out the primary jets and air bleeds with it. Ugh. At least I never did that. I had some 90 air bleeds which I figured were close enough, knowing that slightly smaller air bleeds wouldn't hurt anything. At least I was right about that and didn't start drilling out all my 70s. That would have been stupid.

I did test drill a set of 70 air bleeds once with the 118 drill bit. It ruined them. No tip-in anymore but the mixture didn't lean out all that much either. I set these ruined air bleeds aside for some future work to machine/drill out and tap for a set of hitachi pilot jets drilled to .68mm. I've got an SA carb here that might benefit from them.

The primary air bleeds are much more difficult to do than secondaries. The differences in head size make it pretty obvious. I've successfully done one set so far.
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Old 09-08-15, 04:32 PM
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The Brain Dump continues! Thanks J9 and Jeff for the recent details, they've been duly recorded.

Jeff I think it would be interesting to do a direct comparison of a stock Nikki, a Jeff Hogged Nikki and a Farrell Hogged Nikki on the same platform by the same driver using the same criteria. The logistics are significant but doable, please see my pm for the plan.

Thanks!
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Old 09-08-15, 11:46 PM
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I feel I have to weigh in.

Jeff - I respect your knowledge and the amount of time and effort you put into your research. I'm not a "Sterling Worshipper" but I do think you've got a bit far in your criticism in some cases.

Take the thinned throttle shafts for instance. Yes, one can argue that weakening the throttle shafts for the sake of a few CFM of airflow is a bad trade off, or not, but the effect isn't zero. I have run three different Sterling carbs throughout the years. My first one was one of his earliest ones, it was zinc-plated and only flowed in the mid-high 300cfm range. It ran very well and didn't have the thinned throttle shafts. As I traded up to his newer carbs, I spent a lot of time talking to him about his design changes and the choices that he made, since his early carbs ran so well I wondered why bother to change it? One of the reasons that there was such an intense pursuit of airflow was not because it was needed - no, even Sterling himself posted the math that proved that it wasn't - it was because the primary competition for the Sterling carbs was the Racing Beat Holley 465cfm carb. There were a LOT of people who wouldn't even bother to buy a Sterling unless it could flow as much as the Holley 465, and Sterling was sure that there was a way to do it without sacrificing vacuum signal, or drivability. He refused to bore out the venturis to the point where they would flow for flow's sake while sacrificing vacuum, so him and Carl pulled out every trick they could to get their carbs to that point.

Necessary? Not to anyone who understood how to turn displacement x RPM into max airflow requirements. Detrimental? Not as long as you were careful and followed his instructions on throttle adjustment. I've never had a solid throttle-stop and haven't managed to bend mine. But when you're marketing your product to the unwashed masses, sometimes you have to get the flashy numbers for the folks who think numbers are everything. Plus, he didn't hide any of that - there are still posts of his around where he explains why you don't need a 600cfm carb or even a 465cfm carb on a 12a or 13b.

Also, you seem to have a slightly different idea of which members of the Carl/Sterling team did what. Yes, Carl had the flowbench and Sterling didn't. Beyond helping with the flow testing and some assembly and plating work at the beginning, Carl wasn't heavily involved in Sterling carb research, development and production throughout most of the run. The idea that if Carl didn't know something Sterling didn't either is pretty far from the truth. Carl was a smart guy, but Sterling was the one waist-deep in airflow theory, and the carb that bears his name was his brainchild.

Sterling did know that airflow testing on a bench and real world performance and driving were different beasts altogether. It's one of the reasons that I spent a long weekend driving down into the 'states so that him and I could take my car to a dyno two states over and test jetting changes. It's unfortunate that we didn't get even more dyno time to try all sorts of different mods, but we made the most with the time we had.

The unfortunate truth about why his carb making went downhill was that life got in the way. I'm not here to make excuses for him, nor do I think that anyone should need to defend him a decade after the fact. But since he's not here and nobody else that's still around seems to have known him at the time I feel I've got to at least put some context around what happened.

Sterling tried hard to turn his passion and his hobby into something that he could live off of, but the amount of time, money and effort that went into each rebuild had him barely breaking even most of the time. The volume of demand was WAY too much for him to take alone, and he wasn't making enough to support his family off the carbs, let alone hire help building them. So most of the time he had to take a regular day job to make ends meet and do the carbs on his off hours. He took more orders than he could fill in a reasonable time because he didn't want to turn customers away, but that led to him getting months and months behind. Customers would (rightfully) get frustrated at the wait, file paypal disputes to get their money back, and he'd end up with paypal funds frozen and having to refund cash that he had already put into parts, powerdercoating, etc...

Some life circumstances resulted in him having to move to a smaller house where he converted an unheated shed into his workshop. I don't know if you've spent much time in the north-east, but working in a shed by a propane space heater in the middle of February isn't fun. Still, he kept at it.

The point where **** started to get really bad as you eluded to was when he stopped being able to street test his carbs. I can't remember exactly what took his FB off the road first, but I know that a combination of a blown transmission, wiring issues, and exhaust issues (which the local police didn't take kindly to) took his car off the road, then I think it was blown side seals that stopped him from being able to even run carbs in his driveway. Barely able to make ends meet as it was, he couldn't afford to get it going again and started building and selling carbs untested. Not a great idea, but he was already months behind and felt that he had to keep producing.

Add to that some personal medical problems that he had (which I won't go into detail about out of respect) and the fact that the forum was pushing to get him to pay vendor fees, and he eventually decided to get out of the carb business altogether, but not before he had a lot of frustrated customers and had driven his own reputation into the mud.

As I said, I'm not trying to make excuses for him. A lot of these decisions were undoubtedly the incorrect ones to make in retrospect. I'm just trying to add context that the kinds of things that brought down Sterling's carb business are the kinds of things that could happen to any one of us who tried to start our own business based on a hobby without prior business management experience. Or even with that experience things like medical issues/expenses, the wife losing her job, the car breaking down, etc... could do anybody in.

He was a hobbyist who tried to turn his hobby/passion into a business and got in over his head. Each person should make their own decisions about Sterling based on their own personal experiences. I don't expect the people who paid and never got a carb to give him a pass on that. But bringing up those kinds of things 10 years later isn't necessary. If you want to promote your own carbs, educate people, and explain objectively why your carbs and your design decisions are better than the ones Sterling or Yaw made like in your first post, that's fine. But when you start building a straw man of them and making assumptions about their "misguided" decisions, rolling your eyes and saying that they used flowerly language and "faux physics" to cultivate a following, that's when things start to go to far.

Originally Posted by Jeff20B
By faux physics I'm talking about how a flow bench is the same thing as an actual carb on an actual engine, and how the similarities are undeniable.
I'd love to see where he said those were the same thing. He was always very clear with me that they were separate, and that the pursuit of a 465cfm airflow was secondary to the pursuit of performance and driveability. If he'd had the money for more of his own dyno time or a real wideband O2 sensor I know he would have made good use of both of those things to improve his product.

Originally Posted by Jeff20B
I'd say far worse things than simply mentioning his strange manic-depressive behavior in his posting style and how he took on too heavy a work load and then would come on the forum to complain about it, as if that's supposed to satisfy his customers or something. Customers who spent like 400 bucks and then never received a carb. Who does that? Or before he stopped delivering carbs, he'd make you wait 6 to 8 months as I recall. And the carb that would show up wouldn't even idle, or it would flood because he would swap out the nice OEM needles and seats to swap in the garbage parts included in all rebuild kits.
Was any of this really necessary to write? Are you or the people reading this thread gaining anything from this? I'm not saying it's untrue, I'm saying that it's unnecessary negativity over something that's more than a decade past. What does this add to your post that it wouldn't have if you left it out?

Originally Posted by Jeff20B
I certainly do not thin my throttle shafts because as you know it weakens a part that needs to stay sturdy for boost. I like a reliable part that I know will perform whether I lightly floor it, or I mash the pedal. I also know it will consistently work in all temperatures because as you might know, when things heat up and parts expand, the distance the throttle cable must travel to fully floor the carb will change and cause the pedal stop Yaw and Sterling carbs require, to either not open the throttle all the way, or tend to open it further than intended due to the adjustment having been set on a cold engine. Then you end up with a bad idle because one butterfly is open more than the other thanks to a twisted throttle shaft.
You were making a carb for boost, he was making carbs for the folks that were buying Holley 465s. Yes, with more research and a turbo at his disposal he could have made a carb that performed well at both and it wouldn't have had the shaved throttle shaft. Different design decisions made for different reasons. It doesn't make his "wrong", it's just a different set of trade-offs. Many would agree that your trade off is the preferred one and I wouldn't argue. As for the hot vs. cold stretching of the throttle cable, I think you're reaching a bit with that one. I'd like to see a throttle cable removed from the car, measured cold, then heated and measured again. I'm willing to bet the difference isn't enough to warp the throttle shaft, but I'll eat my words if proven wrong.

Originally Posted by Jeff20B
See, it's little things like that, that folks like Sterling, who seem to need to reinvent the wheel because they can do it better than Mazda, always falter on. But I can tell you exactly why Sterling's carbs didn't want to idle. Aside from any other actual physical problems that I don't know about such as a possible twisted shaft or just a misaligned butterfly or whatever, but knowing these carbs as I do, I can venture an educated guess. Ready for the actual secret? Primary short slow air bleeds.
"...folks like Sterling, who seem to need to reinvent the wheel because they can do it better than Mazda..." - this sounds like you're trying to create an "us vs. them" split where none exists or is necessary. You make the attempt to improve upon an existing design (up to and including re-working/re-inventing it) sound like a bad thing. It's what you do, it's what I do, it's what Sterling did. Criticize his design choices, but this is entirely unnecessary.

I think I should take a sec to mention that my Sterling still runs and idles brilliantly. I never had idle problems with my Sterling carbs that were caused by the carb itself. Sure, I've had every other idle problem known to man from vacuum leaks to intake manifold gasket issues to fuel supply problems and even throttle cable adjustment issues. But you talk about the Sterling carbs as if they never idled well and it was a problem he just couldn't figure out. Head over to my Project Naomi threads, check out the start-up videos, and see the idle on my Sterling after the choke kicks off.

In fairness, he shipped some poorly jetted carbs at the end. My friend Marc got one. I swapped the jet config to match the one I have (that we tweaked on the dyno) and it was fine. Yes, that would suck for anyone who didn't know enough to troubleshoot their own, and yes this was a bad move on Sterling's part. But it was far from an unknowable secret that he failed to unlock.


Like I said at the beginning Jeff, I respect your dedication to the community, your knowledge and the amount of time and effort you put into your research. I don't think you need to belittle Sterling and his design choices to make yours seem better, I think your decisions can stand on their own. It does nobody a favour to re-hash old issues with someone who actually made huge contributions to the community and its knowledge of these carbs. Was he perfect? no, of course not. Did he make mistakes? Sure, who doesn't? But I can't help but leave this thread with a sour taste in my mouth with regards to your treatment of Sterling. If I was a newcomer to the forum, posts like these would have me think that Sterling was a person of questionable character and intelligence whose posts should be dismissed if ever I see them. That's not helpful for anybody.

So keep improving on the work that came before, but remember that it's more worthwhile to concentrate on the deficiencies you see in the carburetors, more than the ones you see in the people.

Respectfully,

Jon
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Old 09-09-15, 04:12 AM
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Jon, I'm glad you got three Sterling carbs and enjoyed them. I'd be honored if someone wanted three of my carbs. I'd think it a bit strange though.

As for the rest of it, I'll chalk it up to my artist's temperament. I find I need to think and act this way to get anything done. Sterling had it too, but it manifested in different ways with different motivations and conclusions. That said, I think my carbs are better. Artist's temperament. Or is it some kind of complex?

I'd like to think I learned from Sterling's mistakes. This is not a business for me and it never will be. I am not competing with RB carbs; I've already surpassed them. Instead of doing damage to the Nikki in pursuit of the unicorn horn of CFM numbers, wankel=awesome and I proved you don't need any fancy pants stuff like flow benches and textbook perfection to make a Nikki better than the RB recommended Holley 465. That was Sterling's goal, and we found a shortcut.

I took it a step further on my 13B testing an RB Holley 600. Sure it wowed me, but so did my carbs when used NA. There is no comparison when you throw boost at it, of course, which I know is like apples to oranges, because you can't easily boost a single pumper Holley. So once again my carbs are better.

I could go on but what this all boils down to is we've successfully shattered the mental construct of a modified Nikki off its high pedestal, originally placed there by Yaw and Sterling, and delivered it to the people where it should have been this whole time. Kinda like how grunge music took over when everyone got tired of the glam rock million dollar over the top music scene. Music needed to go back to the garage and be accessible again. As did the Nikki. I will not apologize for any of it because I feel it needed to happen. I don't own a flow bench and I doubt any of you reading this do.

Building a Nikki to make it better than a Holley is a pretty big deal for some of us. I assure you it wasn't one of my goals, but when I found out mine in fact were better, I had a pretty good day. And we can all do it with some basic shop tools like a die grinder and a dremel. You don't even need a lathe! Of course it doesn't hurt to have one (unless you do it wrong like that SVT guy).

I brought things up from the past because the past is where a lot of these concepts and constructs occurred. You can't have a thread title with the words "hogged out vs boost prepped" without references. Do a forum search for Sterling, bad_83 etc to see precisely what I'm talking about. Sterling = hogged out and bad_83 = boost prepped. You can't argue this point either because these two were known for the carb results they got. At least that's how I remember it. Not going to apologize for this either. And why should I?

Lastly, because its late, and I don't want to type anymore. Ah eff it. It's late and I don't want to type anymore.
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Old 09-09-15, 06:00 AM
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my .02 cents on the sterling carb thing

When I was actually looking to buy one, I only found a few. 2 of 3 potential sellers warned me that their carbs had issues since the day they got them. Both of them commented that it wouldnt idle correctly, and that they were underwhelmed by the lack of polish in its tuning.

Those were my reasons for just building my own. Even the owners of them werent really in love with them.

This speaks volumes to me after the truckload of crap ive been through with RB over their 465 product. Some people swear they were perfect out of the box (impossible) and loved them dearly. I had a totally different experience where I ended up buying 2 of them before I realized they were just a crappy execution of a 4bbl. Not only that, an employee at RB even went out of their way to make it an even worse experience than it already was...

So when I have personal experience with something, and I see someone claiming something I know isnt true, it makes me wonder. As many people who had trouble with Sterling and his product and theres still people to defend him. Theres just no way a Sterling could have run or idle properly on the street with the air bleed arrangement he was running. And if it DID run well enough to be liked so much, perhaps sometimes he actually did something different. Or maybe he changed something along the way. Or maybe he didnt.


I have my reasons to believe the guy knew what he was doing, but failed to *always* implement the knowledge he had. Its kindof like working with engineers. They are some of the smartest people on the planet, but they rarely go a full day using that beautiful brain of theirs. They make some of the simplest mistakes if any of us.
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Old 09-09-15, 07:54 AM
  #24  
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Whoa there, engineers never make mistakes, NEVER!





except in the afternoon sometimes.

A quote from a an guy I work with and respect a lot:

"I try to make all of my mistakes before noon."

The point being, if he makes them early he still has time to fix em the rest of the day.
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Old 09-09-15, 10:15 AM
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Originally Posted by vipernicus42 View Post
One of the reasons that there was such an intense pursuit of airflow was not because it was needed - no, even Sterling himself posted the math that proved that it wasn't - it was because the primary competition for the Sterling carbs was the Racing Beat Holley 465cfm carb. There were a LOT of people who wouldn't even bother to buy a Sterling unless it could flow as much as the Holley 465, and Sterling was sure that there was a way to do it without sacrificing vacuum signal, or drivability. He refused to bore out the venturis to the point where they would flow for flow's sake while sacrificing vacuum, so him and Carl pulled out every trick they could to get their carbs to that point.
this whole "sterling carb" thing to me was funny. i've been around enough to remember the Yaw carb, and i know that sterling took over after that, but Rotary engineering offered a 465cfm nikki, and then even racing beat used to do them, way way way way back. basically people have been modding nikki's since day 1.

secondly while he was correct about the total airflow needed, ~300cfm, he was applying the equation incorrectly. if the stock carb was on an open plenum intake, like a v8 he would have been correct, as those carbs have a more constant flow. the stack carb, however is set up to be an individual runner carb, and as such the flow is not steady. i wish i could find an equation, but in an individual runner setup the carb has to meet the instant demand of the rotor/piston. i guess the proof is that even though the stock carb flows enough, power goes up when you increase flow.

third. my friend bought one, and UPS damaged it, so he ordered another. the bent one was an early one, and the second one was one built near the end. the difference in build quality was pretty big. the early one was plated, and the late one was painted after it was assembled. oh and the second one didn't work. i ended up having to take the first one apart and use pieces to make it work. it runs ok, power is better, but it has that part throttle miss that they seem to have. to his credit, Sterling was on the forum still, and he was helpful.

conclusion? well the conclusion was that you can make these carbs yourself, its very very easy to look down the barrel and see all the S*%T in the way of airflow! as an aside, i thinned the throttle shafts, if you open the throttle and look in there, the shaft takes up so much space, you don't need to remove it like Mr Yaw did, but it certainly doesn't need to be a 10mm steel shaft either
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