black82gsl

iTrader: (3)

I got another nikki off a sa in the bone yard so u want to try to do the "sterling" thing since he doesn't build them any more. I've done a lot of research and know mostly what to do. Main question is how far to bore out the venturi's? I know it's not a lot but I'm looking for a actual measurement. I've read a lot of old threads an there's a few different specs Im seeing. And also says to just drill the jets out with a 1mm drill?

Jeff20B

iTrader: (13)

On my 4 port 13Bs I've gone to 24.5 up to about 24.9mm. The primary jets needed to be upped to match the incoming air. I had a 118mm drill bit and it fit the bill, for the most part. For 24.5mm venturis, I'd say 115 jets would be best, while the 24.9mm prefered a set of 120 jets I had from another Nikki. Still another Nikki with a set of 24.7mm venturis liked the 118 drilled jets just fine.

I didn't touch the secondaries and they're happy with the stock 160 jets and 140 air bleeds. This was important for boost as I didn't want to screw with the air/fuel curve here.

Speaking of air bleeds, I had a couple sets of 90 primaries I grabbed out of some old 79 Nikkis that worked great.

If all you have are a set of 80s, they should work ok too. The 70s are a little small and will fatten it up more at the top end. Stay way from the 60s.

Get a wideband, of course.

I also do the Sterling accel pump mod but go with a hole spread of 1 1/8", not his recommended 1 1/4" on the piece of extension steel you need to add, and use the 79 style accel pumps that come in the hygrade rebuild kits as they have more travel than the 81-85 style. You need slightly longer screws and three gaskets on either side. Sterling does a good job explaining what/how to do everything.

I also remove the choke flapper and fill the two holes with quicksteel. I retain the fast idle linkage because there is no reason to get rid of it, and it can still serve a purpose. The nice thing about a modded Nikki like this is it's very easy to start cold and keep running with your foot so a choke is not even needed anymore.

The one mod I don't touch is the throttle shaft machining/thinning. I don't like the idea of removing the butterflies (disturbing the critical hold down screws that could fall into the engine later and possible damage to the butterlies during removal/install etc) and then you're left with a very fragile shaft that can twist pretty easily. Some others prefer this mod over even the venturi mod and I'm like why? My venturi modded Nikkis without the shaft mod flow plenty on a 74 ported 13B whether NA or turbo so I see zero point in the shaft mod, but sometimes you gotta do what you gotta do, you know? If it fails, it was a learning experience, but if it worked, hey you got away with it. Good for you. It's just way too far into the risk vs reward zone for me though.

black82gsl

iTrader: (3)

Good info. I'm running a stock port 12a for now so what do you think on that?

Jeff20B

iTrader: (13)

Hmm, I'd say don't go any bigger than 24.0mm because I tried my 24.9mm carb on a 74 ported 12A on top of a cleaned up FB manifold (the ones that don't flow worth anything) and it had a decent exhaust consisting of an RB header, collected to 2.5" through a Magnapack 18" 4" round acting as a presilencer, then contracted down to 2" the rest of the way and through an aftermarket OEM stockish style muffler.

This setup was running a stock Nikki. It ran and drove well enough but I assumed my modded Nikki would wake it up like it did on my 74 ported 13B with the RB long primary exhaust. I was kinda wrong. The 12A didn't respond very much to the modded carb the way I thought it would. I would have ventured a guess that maybe a set of 23mm venturis would have been better, but that's the crappy intake manifold and crappy exhaust talking. So in conclusion I'd just go with 24.0mm venturis because it's what Sterling and Yaw did on their modded carbs. Of course they'd use the better intake manifolds (at least a 79 style but an RX-3 version is vastly better if you can find one) and the RB long primary exhaust.

Oh I'd do direct fire ignition, of course, because it does make a noticeable difference on carbed engines. I prefer DLIDFIS.

And the fuel system is what Yaw harped on all the time. He recommended a setup (don't recall anymore but he had a special expensive gauge that he insisted on) but I've found a much better combo. A mallory fpr and a high volume fuel pump. Either an MSD EFI pump or a Carter carb pump. Either will work for NA. The mallory has a return so it takes the guess work out of setting the fuel pressure. Don't bother with the Holley pressure regs as they are dead-head style and tend to vary in fuel pressure depending on temp and their mood at the time. lol And oh yes get a decent gauge like a typical 1 to 15 psi cheapo or expensive. Liquid filled or not. I've found they both work ok. I'm not a stickler about gauges.

black82gsl

iTrader: (3)

Yeah I'm still running a stock fuel system. Already have dfi.

j9fd3s

iTrader: (3)

this is in semi random order....

so the SA carb top is bigger, and LOOKS like it flows more, but it doesn't. the rest of the carb is fine, and actually having the AIR adjust screw is kind of nice.

paul yaw had you run a special 0-5psi gauge, apparently most gauges are only accurate in the middle of their sweep, so something like an autometer 0-15psi gauge doesn't have enough resolution in the 2-2.5 area that we are running in.

i think Mr Yaw ran a carter fuel pump into a holley regulator, although i'm not sure its super important, and the mallory FPR looks much easier to mount on a car. i'm tempted to run the external walbro carb pump, as it looks like it would be a direct replacement for the stock pump. the carter doesn't fit well.

so the carb, getting more flow is the easy part, flip it upside down, and open the throttle and look down, you'll see that the throttle screws and shafts take up most of the opening!

Mr Yaw thinned the side of the throttle shaft with the threads, and then might cut the other side off with different screws, BUT he also made you build a throttle stop by the gas pedal, so you don't bend s%*t.

i think finding shorter screws would be a big deal for flow, and the carb i built i thinned both shafts a little. its up to you, but since they are so huge you can thin them a lot without taking away the strength, imo.

i remove the choke butterflies too, but i also leave the fast idle bit. i dont need the choke, but the fast idle is nice.

i'd follow jeffs advise for the venturis and jets, he's spent a lot of time playing with these. if theres any easy tuning advise its to start rich, like it doesn't run rich, and then lean it out, until its as fast as it goes, and then richen it up 1-2 jets. you wanna be on the rich side of fastest

black82gsl

iTrader: (3)

Well I'll give it a go and see what happens. I still hav my stock carb to fall back on. Now that I'm use to my car it feels like a snail. I'm planning on a header to go with the carb. And I asked this on a different thread but didn't really get any clear answers. Shoul I use the sa intake or just stick with my stripped fb one? I have the shutter valve removed and machined that side to match other.

wankel=awesome

The older carb with the larger choke horn is pretty much the same imo. I used both when modding my own nikkis and felt no differences between the 2 when they were "done". The older carb was actually easier, and cleaner because of the old school fuel bowl vent and total lack of solenoid that mine had. When you are opening up your top cover on the FB carb, you actually take a good bit of material away from the primary side to help free up the flow through the carb (I copied early "420 cfm" yaw carbies). With the older carb, you dont need to. And you can retain its choke because of this, if you want it.

After you get the throttle shafts, and the venturi size opened up its sorta just works and makes more noticeable power. Which I honestly believe is the biggest difference one can make to the Nikki in terms of more airflow easily. The manifold is also critical, as the late model FB stuff manis suck a LOT. In a bad way. I ported a couple to be as visually satisfying as an SA mani, but ill never know if it flows as well or not. But, I can tell you its a clear difference by switching from the FB manifold to the SA manifold...

Then the biggest "Sterling" things are the easy stuff like acc. pump and mech secondaries. You dont need mech secondaries, but to some people its required. I have vac secondary carbs that have zero bogs on opening and open nice and quick and dont hesitate, which I couldnt do with the mech secondaries 100% of the time. Sometimes it was perfect, and then other times id push it a little too far at lower RPM's and start to bog it down. The Vac secondaries minimizes that, and if tuned properly I believe are 90% as effective as the mech secondaries.

Tuning it is easy, especially if you invest in a pin vise set and drill/tap your own restrictions. (Just like the Sterling)

If I could afford to produce what I have built for my own car, I think it would be on par with the Sterling. It wasnt expensive, but it is time consuming and requires a good bit of tooling to do it right every time.

And on the throttle shaft screws, button head torx screws workwell and can be easily trimmed to length and are pretty hard to over torque and ruin those delicate thinned throttle shafts! I was going to try counter-sunk torques, but I ultimately ran out of tinker time and just went with button heads.

The Nikki is a lot of fun, hope you enjoy it and learn a lot from it haha.

black82gsl

iTrader: (3)

Thanks a lot for the good info man. I'll for sure grab the sa intake then.
As far as the choke goes..... My carb now is all rebuilt and stripped down. When it's below 50 out side it doesn't like to start with out the choke. Whats up with that? My old rb set up on my old car never needed a choke. So was kinda scared to run no choke but like u said should be ok on the older carb? What about sharpening the leading edge of your butterfly plates? In my head it seems like that would help some?

wankel=awesome

They are thin enough stock haha.

idk about your experience, but my nikki's run lean on 12a's that have stripped emissions and header/free flow exhaust. The need for a choke gets more obvious the leaner the warmed up air/fuel mixture is. You dont *need* a choke, because you can just pump fuel down the engine by pumping the throttle, which will help it start, but the fast idle+richer mixture with a functional vacuum pull off is pretty nice for nice quick and easy start ups and normal driving before the engine is warmed up.

And it might be just me, but I like the simplicity of the earlier carbs. If i had to choose which to personally mod for myself id run the older one just because theres less crap on the carb to remove. They are harder to get gasket kits for, but they have their advantages. I believe the 79-80 carbs had the 140 high speed air bleed on the secondaries too, which is desirable.

If you want an early carb/SA intake mani let me know, I have both just sitting around waiting to fund my next car.

wankel=awesome

Also, how far are you away from Volk Field? I have my 85 up there right now lol.

black82gsl

iTrader: (3)

You talking about the national guard place? If so hour and a half. I'm not sure what year the carb I have came off just know it was a sa. I know of another that I can get another intake and carb. I actually found 3 junk SA's in a feild but lady hasn't called me back about them. I guess there been siting for like 16 years?

wankel=awesome

Yeah, Volk Field is a national guard location. My FB is still up there from when I was at Fort McCoy. Just waiting on it to ship back down here with TMO.