Mallory 4309 fpr vac/boost nipple question (boosted Nikki)
01-16-15, 05:17 PM
#76
Yeah, just aim for 200HP. It's double stock HP like you said. It's fun, practical, it won't break anything if you don't do anything stupid, and it will or should be able to break the tires loose just about any time.
Traction might be your number 1 concern, especially in colder weather.
If you get stickier tires there is some danger to the diff and/or axles, or the clutch might slip. Something's gotta give. I'd rather it be the tires. 
Whatever you do, don't mod your car too much like DirectFreak because it gets way too expensive and you're left with a car you don't want to drive anymore.
So don't chase the unicorn horn of 400HP or whatever. See how 200HP treats you, and if it's still not enough, make 250 or 300 your goal, but know it's a slippery slope.
I'm only planning on no more than 270HP because that's double the stock GSL-SE's 135HP, but I might not get there because I'm having way too much fun at stock S5 wastegate spring pressure of 7psi or so. Actually just today I read something in the FC section where a guy stated the S4 and S5 are both at 5.5psi and the S5 has some sort of boost solenoid controlled by the ECU which gets it closer to 9psi. That's the first time I've ever seen that info, so no way to know whether it's true. Heck maybe my setup with a stock wastegate size, which is known to be small, and a full 3" exhaust, is experiencing boost creep.
Here's a link. https://www.rx7club.com/2nd-generati.../#post11856428
Traction might be your number 1 concern, especially in colder weather.
If you get stickier tires there is some danger to the diff and/or axles, or the clutch might slip. Something's gotta give. I'd rather it be the tires. Whatever you do, don't mod your car too much like DirectFreak because it gets way too expensive and you're left with a car you don't want to drive anymore.
So don't chase the unicorn horn of 400HP or whatever. See how 200HP treats you, and if it's still not enough, make 250 or 300 your goal, but know it's a slippery slope.
I'm only planning on no more than 270HP because that's double the stock GSL-SE's 135HP, but I might not get there because I'm having way too much fun at stock S5 wastegate spring pressure of 7psi or so. Actually just today I read something in the FC section where a guy stated the S4 and S5 are both at 5.5psi and the S5 has some sort of boost solenoid controlled by the ECU which gets it closer to 9psi. That's the first time I've ever seen that info, so no way to know whether it's true. Heck maybe my setup with a stock wastegate size, which is known to be small, and a full 3" exhaust, is experiencing boost creep.
Here's a link. https://www.rx7club.com/2nd-generati.../#post11856428
I've had a stock S4 turbo and boost creep was a problem in really cold weather. It would occasionally trip the fuel cut. The S4 wastegate is pretty small. Stock boost was normally about 6 psi in good weather.
I have stock S5 turbo in my vert. It hits about 7-8 psi with the stock wastegate and no boost controller hooked up. It has mostly Jspec S4 electronics though.
I ported the wastegate on the FB's S5 turbo. I just enlarged it enough so that the stock flap could barely cover it. So I get 4-5 psi at full boost. Can't wait to nudge that up a bit.
01-18-15, 09:18 PM
#77
Tried stock 160 secondary fuel jets with the plugged slow air bleeds. No good. AFR's hit a lean brick wall as soon as I started to build any boost. So I'm swapping the slow air bleeds back to stock and I'm going to try making smaller main secondary air bleeds.
Jeff, you're using Holley Dominator air bleeds threaded into your stock bleeds, right? Do you remember what size bit and tap you used to make those?
Jeff, you're using Holley Dominator air bleeds threaded into your stock bleeds, right? Do you remember what size bit and tap you used to make those?
01-19-15, 12:15 AM
#78
I don't recall the bit size because it came with a tap and drill set. I just used the bit that matches the tap. The tap is a 10-32. Hope that helps.
Actually, I can help you a bit more. I needed to use two taps. One is a regular tapered style. Start with this. The other is what's called a bottoming tap or a blind hole tap. It is really hard to start with because it has no taper. But this allows you to cut threads all the way to the bottom of your hole. Important here as there isn't a lot of room for threads. You may recall a few weeks ago when I accidentally drilled one too deep and the thread cutting process caused the emulsion tube to break off. So don't go too deep and uoi need to get two taps. Heck get two regular taps and grind the taper off of one.
Actually, I can help you a bit more. I needed to use two taps. One is a regular tapered style. Start with this. The other is what's called a bottoming tap or a blind hole tap. It is really hard to start with because it has no taper. But this allows you to cut threads all the way to the bottom of your hole. Important here as there isn't a lot of room for threads. You may recall a few weeks ago when I accidentally drilled one too deep and the thread cutting process caused the emulsion tube to break off. So don't go too deep and uoi need to get two taps. Heck get two regular taps and grind the taper off of one.
01-19-15, 09:15 PM
#79
I don't recall the bit size because it came with a tap and drill set. I just used the bit that matches the tap. The tap is a 10-32. Hope that helps.
Actually, I can help you a bit more. I needed to use two taps. One is a regular tapered style. Start with this. The other is what's called a bottoming tap or a blind hole tap. It is really hard to start with because it has no taper. But this allows you to cut threads all the way to the bottom of your hole. Important here as there isn't a lot of room for threads. You may recall a few weeks ago when I accidentally drilled one too deep and the thread cutting process caused the emulsion tube to break off. So don't go too deep and uoi need to get two taps. Heck get two regular taps and grind the taper off of one.
Actually, I can help you a bit more. I needed to use two taps. One is a regular tapered style. Start with this. The other is what's called a bottoming tap or a blind hole tap. It is really hard to start with because it has no taper. But this allows you to cut threads all the way to the bottom of your hole. Important here as there isn't a lot of room for threads. You may recall a few weeks ago when I accidentally drilled one too deep and the thread cutting process caused the emulsion tube to break off. So don't go too deep and uoi need to get two taps. Heck get two regular taps and grind the taper off of one.
02-27-15, 01:36 PM
#80
I have an update. I redid the fuel system with a 5/16" send and a 3/8" return. Now the mallory can be adjusted properly to 2.5psi. It can go all the way down to 1psi. It also doesn't want to flood the carb under spirited driving in vacuum anymore. Two problems solved!
I haven't gone into boost yet because the turbo is a fresh rebuild and the clutch was just changed. I think they need some miles first. It feels very strong though. I highly recommend my setup to anyone.
It also doesn't want to flood the carb under spirited driving in vacuum anymore. Two problems solved!I haven't gone into boost yet because the turbo is a fresh rebuild and the clutch was just changed. I think they need some miles first. It feels very strong though. I highly recommend my setup to anyone.
02-28-15, 01:26 AM
#81
I tapped the venturis out of one of the carbs for additional hogging. I went for 25.1+mm this time. They vary from 25.08 at the smallest to 25.18 at the largest and about 25.15 average. This is to test something peejay said about how the small venturis like stock and Sterling (20mm and 22mm respectively) actually hurt low end torque.
This goes against Sterling and Carl's findings on the flow bench, but says nothing about their real world driving experiences, which from my understanding, was apparently pretty limited to just Sterling's stockported 12A with an RB long primary, and whatever Carl was driving at the time, and also feedback from customers who didn't have access to any other larger hogged Nikkis and only had their stock carbs to compare (or the typical aftermarket carb with their share of issues). Sterling also did several dyno runs testing different tunes (jet and air bleed combos) but not different venturi sizes, if I'm remembering his website correctly. Just his best "cut", according to Carl's flowbend testing results, was all he ever used from that point on, as he was confident it was the best compromise between flow and vacuum signal strength.
Well it turns out my simple hogged-by-hand venturis have been more than amazing compared with any stock carb I've ever tried, and quite on par with RB's Holley 600, only without the usual carb glitches, and better than PercentSevenC's weber in every way. And the beautiful part is mine are all as tuneable as Sterling's without all the flip-o-matic bells and whistles which aren't necessary on a boost prepped carb anyway. I'm telling you guys you need to mod your own Nikkis. It's very rewarding.
peejay said something about how the small venturis right above a separate runner manifold (it's not an open plenum like other engines have, but we do have channels) where each barrel is above a runner, have such a strong reversion pulse that it stalls out the flow for so long that by the time the runner is flowing the correct direction again, the venturi is so small that it runs out of time before the next reversion pulse hits. That is why larger venturis have better low end torque because they are less effected by it. I might have mangled the explanation but I think I got it right.
I've already had a bit of experience proving peejay right and Sterling wrong with two carbs with two large but different venturi sizes and two different uses (NA and boost). One carb has 26mm venturis used for NA and the other has 24.9 tested with boost and NA. When both carbs were NA, they both had excellent low end grunt which is totally opposite what Sterling would have you believe; the 26mm being the more powerful one. I didn't hog the 26mm one by the way, and not sure my tools can cut that far. It was like that when I got it.
As for the boost prepped carbs, they range from 24.9 down to 24.5 and I gotta say, the 24.5 was the baby of the bunch. So I decided to hog it out to 25.15mm to see what it can do. I bet it will drive nicely and have more power than I know what to do with.
This goes against Sterling and Carl's findings on the flow bench, but says nothing about their real world driving experiences, which from my understanding, was apparently pretty limited to just Sterling's stockported 12A with an RB long primary, and whatever Carl was driving at the time, and also feedback from customers who didn't have access to any other larger hogged Nikkis and only had their stock carbs to compare (or the typical aftermarket carb with their share of issues). Sterling also did several dyno runs testing different tunes (jet and air bleed combos) but not different venturi sizes, if I'm remembering his website correctly. Just his best "cut", according to Carl's flowbend testing results, was all he ever used from that point on, as he was confident it was the best compromise between flow and vacuum signal strength.
Well it turns out my simple hogged-by-hand venturis have been more than amazing compared with any stock carb I've ever tried, and quite on par with RB's Holley 600, only without the usual carb glitches, and better than PercentSevenC's weber in every way. And the beautiful part is mine are all as tuneable as Sterling's without all the flip-o-matic bells and whistles which aren't necessary on a boost prepped carb anyway. I'm telling you guys you need to mod your own Nikkis. It's very rewarding.
peejay said something about how the small venturis right above a separate runner manifold (it's not an open plenum like other engines have, but we do have channels) where each barrel is above a runner, have such a strong reversion pulse that it stalls out the flow for so long that by the time the runner is flowing the correct direction again, the venturi is so small that it runs out of time before the next reversion pulse hits. That is why larger venturis have better low end torque because they are less effected by it. I might have mangled the explanation but I think I got it right.
I've already had a bit of experience proving peejay right and Sterling wrong with two carbs with two large but different venturi sizes and two different uses (NA and boost). One carb has 26mm venturis used for NA and the other has 24.9 tested with boost and NA. When both carbs were NA, they both had excellent low end grunt which is totally opposite what Sterling would have you believe; the 26mm being the more powerful one. I didn't hog the 26mm one by the way, and not sure my tools can cut that far. It was like that when I got it.
As for the boost prepped carbs, they range from 24.9 down to 24.5 and I gotta say, the 24.5 was the baby of the bunch. So I decided to hog it out to 25.15mm to see what it can do. I bet it will drive nicely and have more power than I know what to do with.
02-28-15, 10:46 PM
#82
Bigger return FTW. These carbs don't like a lot of pressure do they?
I'll back up the not-machine-shop-perfect hogged venturis. I only used a quarter to measure my secondaries. I just kept grinding so it fit the same on each side and eyeballed the taper. According to the U.S. Mint, my secondary venturis are 24.26mm! Not sure what I used for the primaries. I wish I could have dynoed it while it was N/A.
An update on mine.... it got an exhaust system today! I finally found a shop that would do a 3" custom stainless setup. They had it done in an hour and a half. I still have a leak between the engine and turbo since I'm using the stock gasket, but it's already soooo much quieter. I used an RB pre-silencer with Flowmaster turbo muffler.
I successfully drilled the secondary main air bleeds and threaded in the holley jets. I got a set with a .58mm opening, and I left them that way for the first test. I left the plugged slow air bleeds in as well, and used my 198 fuel jets. This was still too lean for 5psi: AFR's hit high 12's and there was a bad lean spike and stutter when I hit the gas. So I'm thinking for the next run, I'll put stock slow air bleeds back in and try upping the fuel jets just a bit. If that doesn't work, I'll have to order even smaller jets for the main air bleeds. This thing is hungry.
I'll back up the not-machine-shop-perfect hogged venturis. I only used a quarter to measure my secondaries. I just kept grinding so it fit the same on each side and eyeballed the taper. According to the U.S. Mint, my secondary venturis are 24.26mm! Not sure what I used for the primaries. I wish I could have dynoed it while it was N/A.
An update on mine.... it got an exhaust system today! I finally found a shop that would do a 3" custom stainless setup. They had it done in an hour and a half. I still have a leak between the engine and turbo since I'm using the stock gasket, but it's already soooo much quieter. I used an RB pre-silencer with Flowmaster turbo muffler.
I successfully drilled the secondary main air bleeds and threaded in the holley jets. I got a set with a .58mm opening, and I left them that way for the first test. I left the plugged slow air bleeds in as well, and used my 198 fuel jets. This was still too lean for 5psi: AFR's hit high 12's and there was a bad lean spike and stutter when I hit the gas. So I'm thinking for the next run, I'll put stock slow air bleeds back in and try upping the fuel jets just a bit. If that doesn't work, I'll have to order even smaller jets for the main air bleeds. This thing is hungry.
03-01-15, 12:53 AM
#83
Was it you who was having all kinds of trouble with trying to get a Walbro to work with a Nikki? All kinds of resistors and resitrictors? I had to give up on my Walbro when the lowest it could go was 5psi. The MSD could get down to 2psi but wasn't consistantly that low. Then the fuel line redo is what fixed the problems. But I'm sticking with the MSD pump. It's just too good-working.
I used two washers, one at 25.4mm and one a little bigger to check the ID as I was hogging them out. Kept at it until I got them the same ID at the same depth/taper. Then gave them a little polish (and I use that word loosely). Just enough to get rid of most of the sanding drum scratches and be kinda nice looking. I think they turned out well.
Um, your stock secondaries should be 26mm. Not sure how you got 24.26mm. Did you mean primaries?
How was it NA? A real kick in the pants like mine? Like tg_farrels?
A flowmaster is chambered or baffled, right? Even though it says it's a turbo muffler, it shouldn't be used on a turbo equipped engine. Turbos want a free flowing muffler with no restrictions. Then again it is at the end of the system so maybe it'll be ok.
I put a little 2.5" restrictor inside the dump tip on my 3" RB universal muffler. It's still louder than I'd like. I might do the RB PR Extreme muffler some day.
If you're still too lean, you shouldn't open up your blocked slow air bleeds because it will let in too mich air creating an even leaner condition.
When I blocked my slow air bleeds, it made my setup go to 10.0 on the wideband in boost so I took out my stock 160 secondary fuel jets and swapped in some 150 jets. Then I took out the stock 140 secondary main air bleeds and swapped in the modded ones with a set of drilled 118 fuel jets (originally 106 from a hitachi but any 92 primary fuel jet will work). I wasn't able to check the wideband because it made so much power I had to keep the car from going sideways.
It's fair to say it got even richer due to the smaller main air bleeds. However it didn't sound unhealthy so until I get a chance to repeat the driving conditions with a turbo buddy who can look at the wideband for me, I'll just leave the drilled 118s and the 150s in there for now. j9fd3s would agree that as long as I'm not hurting the engine, start rich and work lean, then richen it back up a tad and you're done. That's what I'm in the process of doing.
My experience has been different from yours. Your carb appears to need ungodly amounts of fuel while mine needs jets that are actually smaller than stock. This is something of a mystery. And I know you're not the only one as we had bad83 and just about anyone else who ever did a boosted Nikki always saying to go bigger on the secondaries. However I only know of one other person (Robert at RS) who needed leaner jets like I did. Just one person! So I'm in the minority here. I wonder what's going on. Any ideas?
I used two washers, one at 25.4mm and one a little bigger to check the ID as I was hogging them out. Kept at it until I got them the same ID at the same depth/taper. Then gave them a little polish (and I use that word loosely). Just enough to get rid of most of the sanding drum scratches and be kinda nice looking. I think they turned out well.
Um, your stock secondaries should be 26mm. Not sure how you got 24.26mm. Did you mean primaries?
How was it NA? A real kick in the pants like mine? Like tg_farrels?
A flowmaster is chambered or baffled, right? Even though it says it's a turbo muffler, it shouldn't be used on a turbo equipped engine. Turbos want a free flowing muffler with no restrictions. Then again it is at the end of the system so maybe it'll be ok.
I put a little 2.5" restrictor inside the dump tip on my 3" RB universal muffler. It's still louder than I'd like. I might do the RB PR Extreme muffler some day.
If you're still too lean, you shouldn't open up your blocked slow air bleeds because it will let in too mich air creating an even leaner condition.
When I blocked my slow air bleeds, it made my setup go to 10.0 on the wideband in boost so I took out my stock 160 secondary fuel jets and swapped in some 150 jets. Then I took out the stock 140 secondary main air bleeds and swapped in the modded ones with a set of drilled 118 fuel jets (originally 106 from a hitachi but any 92 primary fuel jet will work). I wasn't able to check the wideband because it made so much power I had to keep the car from going sideways.
It's fair to say it got even richer due to the smaller main air bleeds. However it didn't sound unhealthy so until I get a chance to repeat the driving conditions with a turbo buddy who can look at the wideband for me, I'll just leave the drilled 118s and the 150s in there for now. j9fd3s would agree that as long as I'm not hurting the engine, start rich and work lean, then richen it back up a tad and you're done. That's what I'm in the process of doing.
My experience has been different from yours. Your carb appears to need ungodly amounts of fuel while mine needs jets that are actually smaller than stock. This is something of a mystery. And I know you're not the only one as we had bad83 and just about anyone else who ever did a boosted Nikki always saying to go bigger on the secondaries. However I only know of one other person (Robert at RS) who needed leaner jets like I did. Just one person! So I'm in the minority here. I wonder what's going on. Any ideas?
03-01-15, 09:51 AM
#84
So I modded another carb yesterday. Same proceedure as before. You just heat the main body, freeze the venturis with some of that canned air stuff held upside down (one started to fall out on its own!) and hammer them out the rest of the way. They're already hogged out to 24.7mm so it shouldn't take long.
Set them up for hand-hogging (held in the workmate). I only used a dremel with a coarse sanding drum until the shape and ID were obtained, then changed to a fine drum. Then when the deep scratches were gone, I switched to um whatever it's called. That thing that looks like a scotchbright pad on a stick. It left a semi-polished surface. I find this good enough. I'm not sure actual polishing is a good idea here. Any opinions?
They were hogged out to, on average, 25.4mm this time. The manifold this carb goes on is an '76 reverse runner so I needed rather large venturis but not as big as the set done by Dave ******* in the Racing Nikki at 26mm. That carb isn't as refined (but I think it was due to the damaged base plate which I've since swapped but haven't tested yet).
Anyway I think going from 24.7 to 25.4 was a good step up in size that shouldn't require any additional jets or air bleed changes. However it still needs tuning on the actual engine it's going on, so the final tune remains to be seen.
Heat the main body again. I like to use a little blue locktite on the outside of the venturis because as the carb gets hot on a running engine, the venturi effect keeps them colder so I feel a little something in there to keep the venturis from moving around is a good thing. Then freeze them with the canned air. I like to pick them up with a needle nose, align the notch with the hole and tap them in. I use a washer with the proper OD to perfectly fit the venturi, held in a bolt with a nut on each side. Then wipe up any excess locktite (don't use red!) and you're done with this step. I like to let the carb main body cool a bit before installing the boosters etc. Or that is to say it's cool by the time the boosters go in. Whatever. It's your carb; mod as you see fit.
Set them up for hand-hogging (held in the workmate). I only used a dremel with a coarse sanding drum until the shape and ID were obtained, then changed to a fine drum. Then when the deep scratches were gone, I switched to um whatever it's called. That thing that looks like a scotchbright pad on a stick. It left a semi-polished surface. I find this good enough. I'm not sure actual polishing is a good idea here. Any opinions?
They were hogged out to, on average, 25.4mm this time. The manifold this carb goes on is an '76 reverse runner so I needed rather large venturis but not as big as the set done by Dave ******* in the Racing Nikki at 26mm. That carb isn't as refined (but I think it was due to the damaged base plate which I've since swapped but haven't tested yet).
Anyway I think going from 24.7 to 25.4 was a good step up in size that shouldn't require any additional jets or air bleed changes. However it still needs tuning on the actual engine it's going on, so the final tune remains to be seen.
Heat the main body again. I like to use a little blue locktite on the outside of the venturis because as the carb gets hot on a running engine, the venturi effect keeps them colder so I feel a little something in there to keep the venturis from moving around is a good thing. Then freeze them with the canned air. I like to pick them up with a needle nose, align the notch with the hole and tap them in. I use a washer with the proper OD to perfectly fit the venturi, held in a bolt with a nut on each side. Then wipe up any excess locktite (don't use red!) and you're done with this step. I like to let the carb main body cool a bit before installing the boosters etc. Or that is to say it's cool by the time the boosters go in. Whatever. It's your carb; mod as you see fit.
03-02-15, 05:58 PM
#85
I thought the stock secondaries venturis were 22mm? Maybe I am confusing them. I'll have to check next time I fool with it. It was pretty stout when N/A, but I did all my mods at once so I couldn't really tell specifically where the power came from.
The muffler is a straight-through design made for turbo cars, so it should be fine.
I just haven't liked how the car runs with the blocked slow air bleeds. It behaves unpredictably. I tried to mimic your setup but this carb is too different I guess, so I'll go back to what I was trying before. It was too lean but it was very stable. I think the smaller main air bleeds will help me get where I need to be. The difference in our cars might have something to do with manifold. I have a ported open plenum factory manifold with dimples. It could be reducing velocity and causing a weaker signal, thereby pulling less fuel through the carb. Kinda the opposite of what I had in mind. I have a spare lying around, maybe I'll make a smooth one to test out if I have time.
Your idea for taking the venturis out is a good one! I bet they're a lot easier to work on when you remove them.
The muffler is a straight-through design made for turbo cars, so it should be fine.
I just haven't liked how the car runs with the blocked slow air bleeds. It behaves unpredictably. I tried to mimic your setup but this carb is too different I guess, so I'll go back to what I was trying before. It was too lean but it was very stable. I think the smaller main air bleeds will help me get where I need to be. The difference in our cars might have something to do with manifold. I have a ported open plenum factory manifold with dimples. It could be reducing velocity and causing a weaker signal, thereby pulling less fuel through the carb. Kinda the opposite of what I had in mind. I have a spare lying around, maybe I'll make a smooth one to test out if I have time.
Your idea for taking the venturis out is a good one! I bet they're a lot easier to work on when you remove them.
03-02-15, 07:19 PM
#86
carb whisperer
I thought the stock secondaries venturis were 22mm? Maybe I am confusing them. I'll have to check next time I fool with it. It was pretty stout when N/A, but I did all my mods at once so I couldn't really tell specifically where the power came from.
The muffler is a straight-through design made for turbo cars, so it should be fine.
I just haven't liked how the car runs with the blocked slow air bleeds. It behaves unpredictably. I tried to mimic your setup but this carb is too different I guess, so I'll go back to what I was trying before. It was too lean but it was very stable. I think the smaller main air bleeds will help me get where I need to be. The difference in our cars might have something to do with manifold. I have a ported open plenum factory manifold with dimples. It could be reducing velocity and causing a weaker signal, thereby pulling less fuel through the carb. Kinda the opposite of what I had in mind. I have a spare lying around, maybe I'll make a smooth one to test out if I have time.
Your idea for taking the venturis out is a good one! I bet they're a lot easier to work on when you remove them.
The muffler is a straight-through design made for turbo cars, so it should be fine.
I just haven't liked how the car runs with the blocked slow air bleeds. It behaves unpredictably. I tried to mimic your setup but this carb is too different I guess, so I'll go back to what I was trying before. It was too lean but it was very stable. I think the smaller main air bleeds will help me get where I need to be. The difference in our cars might have something to do with manifold. I have a ported open plenum factory manifold with dimples. It could be reducing velocity and causing a weaker signal, thereby pulling less fuel through the carb. Kinda the opposite of what I had in mind. I have a spare lying around, maybe I'll make a smooth one to test out if I have time.
Your idea for taking the venturis out is a good one! I bet they're a lot easier to work on when you remove them.
03-06-15, 11:06 PM
#88
I test ran the biggest carb today. At first it needed a little tweaking of the throttle stop screw and the AF screw. Understandable seeing as I've just increased the venturis a bit.
How does it drive? I'd say it has more grunt than before. You just rev and let the clutch out quick, and it pins you back. Very nice!
But how is the AF mixture now that it's got bigger venturis? Hmm, pretty good. it seems to have a very small glitch right off idle that is there when you rev it. As if the accel pump isn't big enough anymore, or maybe the air bleeds are too big (bigger venturis let more air in, so maybe less air bleed is needed now), or maybe I need to up my fuel jet size by a small amount. It only makes sense, right?
Think about it; if stock is 92 jets with 20mm venturis, and I had decent results at 118* with 24.9mm venturis, on a boost tune, and 130 jets on an NA tune, it makes sense that I'd need to up my fuel jet size to something a little bit bigger whether NA or for boost. Right?
*actually closer to 122 to 123 drilled equivilant
So I'm thinking of either throwing in some smaller air bleeds or some bigger fuel jets now to get past the small glitch which believe me is not that bad, but it puts the carb back to about a 70% tune where before all this venturi enlarging business, was closer to a 90% tune.
The current air bleeds are a set of commonly found 90s from any SA carb. I'm thinking if I had a set of 80s not curently in use, that'd be perfect (they are perfect in the carb I threw them in, so they gotta stay in that carb). However I do have a set or two of 70s and one set of 60s to try!
One thing I discovered playing with air bleeds is the common misconception that they only affect top end. j9fd3s and I discussed this recently. It turns out air bleeds affect the entire AF curve, from low RPM and tip in, all they way up to redline. I admit my tip in is ok but I could always use a little more.
A good way to get more tip in is with some smaller air bleeds, but I've been using them in my boost prepped carbs that are currently tuned for NA use. I'm beginning to think they need to come out now because back when I first was testing these carbs, they still had the drilled 118s in them. This was fine for boost, but way too lean for NA. Turns out 130 was the right size. But I only had one set to share across five or six carbs. A bandaid fix was to take out the 90 air bleeds that worked ok for boost, and swap in some 70s or 60s. This made the carbs at least driveable for testing.
However now that I've gotten a pack of enough 130s to go around, I'm thinking I can go back to the 90 air bleeds and all will be well in the NA world. This frees up the 70s and 60s for boost tuning!
How does it drive? I'd say it has more grunt than before. You just rev and let the clutch out quick, and it pins you back. Very nice!
But how is the AF mixture now that it's got bigger venturis? Hmm, pretty good. it seems to have a very small glitch right off idle that is there when you rev it. As if the accel pump isn't big enough anymore, or maybe the air bleeds are too big (bigger venturis let more air in, so maybe less air bleed is needed now), or maybe I need to up my fuel jet size by a small amount. It only makes sense, right?
Think about it; if stock is 92 jets with 20mm venturis, and I had decent results at 118* with 24.9mm venturis, on a boost tune, and 130 jets on an NA tune, it makes sense that I'd need to up my fuel jet size to something a little bit bigger whether NA or for boost. Right?
*actually closer to 122 to 123 drilled equivilant
So I'm thinking of either throwing in some smaller air bleeds or some bigger fuel jets now to get past the small glitch which believe me is not that bad, but it puts the carb back to about a 70% tune where before all this venturi enlarging business, was closer to a 90% tune.
The current air bleeds are a set of commonly found 90s from any SA carb. I'm thinking if I had a set of 80s not curently in use, that'd be perfect (they are perfect in the carb I threw them in, so they gotta stay in that carb). However I do have a set or two of 70s and one set of 60s to try!
One thing I discovered playing with air bleeds is the common misconception that they only affect top end. j9fd3s and I discussed this recently. It turns out air bleeds affect the entire AF curve, from low RPM and tip in, all they way up to redline. I admit my tip in is ok but I could always use a little more.
A good way to get more tip in is with some smaller air bleeds, but I've been using them in my boost prepped carbs that are currently tuned for NA use. I'm beginning to think they need to come out now because back when I first was testing these carbs, they still had the drilled 118s in them. This was fine for boost, but way too lean for NA. Turns out 130 was the right size. But I only had one set to share across five or six carbs. A bandaid fix was to take out the 90 air bleeds that worked ok for boost, and swap in some 70s or 60s. This made the carbs at least driveable for testing.
However now that I've gotten a pack of enough 130s to go around, I'm thinking I can go back to the 90 air bleeds and all will be well in the NA world. This frees up the 70s and 60s for boost tuning!
03-07-15, 11:36 AM
#90
Why? You're not doing any boost tuning. That's kind of the point of all these posts on here is to educate others about what I did, how I did it, what the results were, and that you can do it too.
No more need for personality (hero) worship like we had on the forum when Sterling and Carl were the only Nikki modding game in town. I don't want to sell any carbs because they take longer to mod than Katy Perry has been on the charts, and I don't have any stock Nikkis coming in.
I'm starting to see why Sterling was selling these things for like $400 or whatever. It feels like that is the bare minimum I would have to ask for selling one of mine (I'd probably ask for more - just letting you know). And then the recent issues LizardFC has had with his boost tune following my advice. I learned just because it worked for me doesn't mean it will work for everybody. Of course maybe he did something wrong and it's screwing up his results. He didn't even pull his venturis before hogging them. I've found that to be impossible. They have to come out and you gotta spend days, well, hours on each one. If you're fast and have good tools, that is. As a noob, don't count on getting it done fast.
We're all Nikki noobs here and I never claimed to be an expert. That's another reason why I'm on here talking about Nikkis all the time, and another reason I don't feel comfortable selling any of them.
The only one I'd consider selling is the 79-80 hybrid that has the somewhat banged up base plate that led to a glitch above idle when it was on the Racing Nikki (it's one I found in the pile back in 2007 or whenever it was). The 79-80's main body is from a good used 79 and the top is from the racing Nikki that had some air flow smoothing mods performed by Dave *******. He also removed the fast idle brass fitting. I happen to like the fast idle because it means you can step out of the vehicle and not have to keep your foot on it while cold. That's why I would consider letting this go, because it doesn't serve my needs. I also swapped in a set of stock needles and seats because the Grose jets and RX-3 floats are too valuable to let go.
Of course the base plate can be swapped out for any other SA carb. But the glitch might not be caused by it. The glitch might have been due to the Racing Nikki's 26mm venturis, and I'm starting to see why as explained in my post above. The 25.6mm carb also has a glitch there but it's way smaller and hardly noticed. So I swapped this suspected base plate to the 79 main body because its venturis are only hogged to 24.7mm and are less likely to have that glitch.
This swap is still untested and is all speculation at this point. I could be way wrong, or I could be almost right. Still interested? I don't think I'd be. lol Just do your 13B.
No more need for personality (hero) worship like we had on the forum when Sterling and Carl were the only Nikki modding game in town. I don't want to sell any carbs because they take longer to mod than Katy Perry has been on the charts, and I don't have any stock Nikkis coming in.
I'm starting to see why Sterling was selling these things for like $400 or whatever. It feels like that is the bare minimum I would have to ask for selling one of mine (I'd probably ask for more - just letting you know). And then the recent issues LizardFC has had with his boost tune following my advice. I learned just because it worked for me doesn't mean it will work for everybody. Of course maybe he did something wrong and it's screwing up his results. He didn't even pull his venturis before hogging them. I've found that to be impossible. They have to come out and you gotta spend days, well, hours on each one. If you're fast and have good tools, that is. As a noob, don't count on getting it done fast.
We're all Nikki noobs here and I never claimed to be an expert. That's another reason why I'm on here talking about Nikkis all the time, and another reason I don't feel comfortable selling any of them.
The only one I'd consider selling is the 79-80 hybrid that has the somewhat banged up base plate that led to a glitch above idle when it was on the Racing Nikki (it's one I found in the pile back in 2007 or whenever it was). The 79-80's main body is from a good used 79 and the top is from the racing Nikki that had some air flow smoothing mods performed by Dave *******. He also removed the fast idle brass fitting. I happen to like the fast idle because it means you can step out of the vehicle and not have to keep your foot on it while cold. That's why I would consider letting this go, because it doesn't serve my needs. I also swapped in a set of stock needles and seats because the Grose jets and RX-3 floats are too valuable to let go.
Of course the base plate can be swapped out for any other SA carb. But the glitch might not be caused by it. The glitch might have been due to the Racing Nikki's 26mm venturis, and I'm starting to see why as explained in my post above. The 25.6mm carb also has a glitch there but it's way smaller and hardly noticed. So I swapped this suspected base plate to the 79 main body because its venturis are only hogged to 24.7mm and are less likely to have that glitch.
This swap is still untested and is all speculation at this point. I could be way wrong, or I could be almost right. Still interested? I don't think I'd be. lol Just do your 13B.
03-07-15, 12:40 PM
#92
carb whisperer
I have a fresh s4 6 port that is getting a microsquirt and 4 bbl TB. Itll use a 4 barrel air valve but retain port injection. Its almost the same thing as peejay's setup.
I dont *need* and engine, but it would be nice to join the 13b in FB club again since the loss of my SE...
BUT, i have very limited experience with EFI so im hesitant to take on the project.
On the other hand, I have a excellent running 12A, that does everything I want it to, except im getting bored of my vac secondaries. Its just an aging pineapple rebuild that i figured wouldnt hurt to pull out and go through this summer.
As far as any of that is concerned, I DO plan to add a turbo in the future, but its a ways off.
The main reason for not going turbo at this point is a lack of trust in my ability to tune the existing carb (holley) to make it work. The AFR's jump all over the place even in street driving so I thik the addition of a turbo to it would be step in the wrong direction..
I loved my stock nikki when I ran it. Flawless other than a lack of power, and a tiny bit of surging here and there.
I have the holley running pretty perfect at this point, but I dont think it will ever have the same polish or smoothness as the Nikki. If its possible, I never found it.
I dont *need* and engine, but it would be nice to join the 13b in FB club again since the loss of my SE...
BUT, i have very limited experience with EFI so im hesitant to take on the project.
On the other hand, I have a excellent running 12A, that does everything I want it to, except im getting bored of my vac secondaries. Its just an aging pineapple rebuild that i figured wouldnt hurt to pull out and go through this summer.
As far as any of that is concerned, I DO plan to add a turbo in the future, but its a ways off.
The main reason for not going turbo at this point is a lack of trust in my ability to tune the existing carb (holley) to make it work. The AFR's jump all over the place even in street driving so I thik the addition of a turbo to it would be step in the wrong direction..
I loved my stock nikki when I ran it. Flawless other than a lack of power, and a tiny bit of surging here and there.
I have the holley running pretty perfect at this point, but I dont think it will ever have the same polish or smoothness as the Nikki. If its possible, I never found it.
03-07-15, 01:16 PM
#93
Well I did take on a few EFI projects and they always left me wanting. The closest setup I did to yours was an S4 NA 6 port with a stock ECU and harness swap. This thing only had tip in and mild power. Nothing special otherwise, but a whole lot of time and effort went into it, for less power and less wow factor than my hogged Nikki. It also doesn't run as smoothly as we were hoping, tends to flood easily etc. I won't do another project like this because it just wasn't worth it in the end.
Then I've done two MegaSquirt installs. They both turned out pretty craptacular because I didn't know how to tune EFI and the guy I helped set one up wasn't able to tune it very well either, even though he had a laptop and a wideband. And he wasn't afraid to use them! He had prior experiencing keeping a boosted weber 13B together, and he lives for computers and video games. His setup just didn't drive all that well and was a whole lot of work to get it all in there. It had a bit more power than my hogged Nikki, but the other issues it had negated any benefits. In fact the guy said if he wasn't moving out of the country, that he'd jump at the chance to do a hogged blow through Nikki like mine! I'm talking about PercentSevenC, so you can do a search to check out his projects if you're interested.
To make a long story short, I am not convinced EFI is the holy grail of next level rotary awesomeness. I think Nikkis are.
Knowing what we know about Nikkis, and the new things we keep discovering, I'd say go Nikki! And keep the 12A and boost it! You already have some working experience with these carbs, plus we know they already run great on a rotary, so you're starting out with a stable platform, and boost prepping is very straight forward with very little guesswork anymore. As long as you get a short list of parts, you should have no trouble adding boost to your 7.
The short list is:
MSD 2225 fuel pump
Mallory 4309 fpr
maybe a surge tank or swirl pot, for safety
5/16" send and 3/8" return fuel hardlines
direct fire ignition
a flywheel that is heavier than alumimum
a turbo that is sizxed well for your engine such as S4 or S5 on a 12A
3" DP but the rest of the exhaust can be 2.5"
carb hat with a boost reference nipple to the mallory
some kind of BOV and a boost gauge hooked to both primary runners of the manifold
79 intake manifold with a steel or brass short plug bolt with a nipple fitting added Heater Water Outlet Plug for 81-earlier rotary engines - Racing Beat
semi-locked distributor for 10 to 12 degrees total advance
Ok the list is longer than I thought it'd be.
One of the first mods you should do to your Nikki is mechanical secondaries. I welded a small tack on the secondary linkage. It's best to take off the base plate and turn it over. Study the linkage first and see where the best place to weld it would be. If you don't have a welder, you can wire them together.
One of the biggest issues with mech secondaries is the glitch or hiccup when they open. Sterling "solved" it by doing his accel pump mod. It worked for me too, but now that I understand more of what's actually going on in the carb, I'd say fill both secondary slow air bleeds with solder, then test your carb. I think it will get rid of the hiccup without needing to Sterling up the accel pump. However once you go boosted, you will need the Sterling accel pump mod because it continues to flow fuel as the secondaries open. This WILL be necessary to avoid the annoying secondary delay I experienced, but later solved through a combination of solder filled slow bleeds, smaller main air bleeds, and the Sterling accel pump mod, but I didn't drill my nozzle out as large as he suggested.
There's more but do the mech sec mod first and tell us how it went.
Then I've done two MegaSquirt installs. They both turned out pretty craptacular because I didn't know how to tune EFI and the guy I helped set one up wasn't able to tune it very well either, even though he had a laptop and a wideband. And he wasn't afraid to use them! He had prior experiencing keeping a boosted weber 13B together, and he lives for computers and video games. His setup just didn't drive all that well and was a whole lot of work to get it all in there. It had a bit more power than my hogged Nikki, but the other issues it had negated any benefits. In fact the guy said if he wasn't moving out of the country, that he'd jump at the chance to do a hogged blow through Nikki like mine! I'm talking about PercentSevenC, so you can do a search to check out his projects if you're interested.
To make a long story short, I am not convinced EFI is the holy grail of next level rotary awesomeness. I think Nikkis are.
Knowing what we know about Nikkis, and the new things we keep discovering, I'd say go Nikki! And keep the 12A and boost it! You already have some working experience with these carbs, plus we know they already run great on a rotary, so you're starting out with a stable platform, and boost prepping is very straight forward with very little guesswork anymore. As long as you get a short list of parts, you should have no trouble adding boost to your 7.
The short list is:
MSD 2225 fuel pump
Mallory 4309 fpr
maybe a surge tank or swirl pot, for safety
5/16" send and 3/8" return fuel hardlines
direct fire ignition
a flywheel that is heavier than alumimum
a turbo that is sizxed well for your engine such as S4 or S5 on a 12A
3" DP but the rest of the exhaust can be 2.5"
carb hat with a boost reference nipple to the mallory
some kind of BOV and a boost gauge hooked to both primary runners of the manifold
79 intake manifold with a steel or brass short plug bolt with a nipple fitting added Heater Water Outlet Plug for 81-earlier rotary engines - Racing Beat
semi-locked distributor for 10 to 12 degrees total advance
Ok the list is longer than I thought it'd be.
One of the first mods you should do to your Nikki is mechanical secondaries. I welded a small tack on the secondary linkage. It's best to take off the base plate and turn it over. Study the linkage first and see where the best place to weld it would be. If you don't have a welder, you can wire them together.
One of the biggest issues with mech secondaries is the glitch or hiccup when they open. Sterling "solved" it by doing his accel pump mod. It worked for me too, but now that I understand more of what's actually going on in the carb, I'd say fill both secondary slow air bleeds with solder, then test your carb. I think it will get rid of the hiccup without needing to Sterling up the accel pump. However once you go boosted, you will need the Sterling accel pump mod because it continues to flow fuel as the secondaries open. This WILL be necessary to avoid the annoying secondary delay I experienced, but later solved through a combination of solder filled slow bleeds, smaller main air bleeds, and the Sterling accel pump mod, but I didn't drill my nozzle out as large as he suggested.
There's more but do the mech sec mod first and tell us how it went.
03-07-15, 07:28 PM
#94
carb whisperer
Well I certainly dont want to be disappointed by what I build for it.
I "sterling'd" a nikki before but I was never sure if I got it "right". I sold it here on the forums over a year ago. It ran well, but I could never solve some of its little problems with the accel pump. And that carb I intentionally left vac secondaries because of how quickly they opened.
I "sterling'd" a nikki before but I was never sure if I got it "right". I sold it here on the forums over a year ago. It ran well, but I could never solve some of its little problems with the accel pump. And that carb I intentionally left vac secondaries because of how quickly they opened.
03-07-15, 08:47 PM
#95
Heck I'm not sure I got any of my carbs right either. All I can do is test a mod and report my findings.
Some mods turn out better than others. For example, turns out hogging the venturis out as large as I did (25.6mm) introduces a very small glitch right above idle that, so far, I've not been able to get rid of*. However I think it's partially due to the low fuel level in the float bowls from today. Just below half way, while running at only 2psi. I'll adjust fuel pressure up tomorrow or the next time I get paid (to go get gas lol) and have some Nikki tuning time, to see if the glitch goes away.† Something tells me it will, but there might always be a narrow flat spot at about 1500 just due to the combination of parts in this setup (manifold, engine porting, air bleeds etc), as other setups don't exhibit this exact behavior. Every car is different.
*When I turn off the fuel pump to run the carb out of gas, which takes about a minute or so, this off idle glitch gets really wide and encompasses most of the rev range. We're talking from right above idle to like 4 or 5 grand and then it smooths out. It's just a faster way to run the carb out of gas before you take the top off for jet changes etc. I'm not sure that this is really the right way to do it, but I feel it's better than having to use a turkey baster or to just flip the carb upside down above an oil drain pan or some other container to get the gas out. The point is the very small glitch this carb has now wasn't noticed very much until it started running at about 2psi with a lower float level, and I'm sure my large venturis have something to do with it. In other words, the lower the float bowl level, the wider the glitch. It could have something to do with the amount of holes in the emulsion tubes as well.
†I nearly ran out of gas while test driving today. This is why the fuel pressure crept down to just 2psi. You could see the gauge move every time a bubble would make its way through the mallory. Good thing my tank has a sump cup. It lets me run the tank way down to just about empty. I used to be able to hear when the fuel pump was sucking air bubbles but now that it is so quiet from the noise isolation mod I did, it makes it harder to tell. Oh well, a quiet fuel pump sure is nice.
Just today I made some tuning changes because it was too lean now with the larger venturis. We're talking 14 to 15 AFR cruise and lousy low end tip in. Also it's harder to start and the idle isn't as good. Not to mention the off idle glitch.
The carb had 90 primary air, drilled 118 primary fuel, drilled 118 secondary air, 150 secondary fuel. This combo worked ok at 24.9mm and 2.5 to 3psi.
Swapped to 70 primary air. This reduced the glitch and added some tip-in, but it was still running a bit lean at cruise. Also the secondaries have a very small hiccup when they open now. Man, I thought I was done with secondary tuning.
Swapped to 60 primary air and decided to try 106 secondary air. This woke up the low end tip-in quite well, but the off idle glitch was still there. It was still lean at cruise but a little bit better than with the 70s. Gotta swap in some bigger primary fuel jets next, I think. Also the secondaries had a weird stumble. Since I was getting super low on gas, I decided not to push my luck with boost so only tested in vacuum after this.
Next I swapped out the 118 primary fuel jets and swapped in some Holley air bleeds that are about 130 metric. Took it for a spin. Um, now it was too rich at cruise, like 11 to 12. The off idle glitch was nearly gone but the low fuel level in the bowls and the 2psi (due to basically running out of gas) prevented any more driving. But I think I got my answer. Maybe keep the current Holley 130s and just swap from 60s back to 70s, maybe?
Since my drilled 118s are actually closer to a factory 122 or so, I figured 125s are pretty close and might not profit me very much if I were to get a set, and since I don't have any 125s just lying around anyway, I decided to keep the Holley 130s in there, and just swap the primary air bleeds from 60 back up to 70. Also swapped the 106 secondaries back to 118. This did the trick!
I decided to risk driving it one more time just around the block and it paid off. The off idle glitch is nearly gone and the low end tip in is still good enough. The slightly larger air bleeds leaned out the cruise to 12 to 13 (and I saw a couple of 14s in there!) which I can live with for now, and it started pretty easy and the idle was able to be tuned back to 12.2 where the engine runs best.
In all, a productive day.
Cliff notes:
•70 pri air, 130 pri fuel, 118 sec air, 150 sec fuel
•ran low on gas and decided to not tune in boost
•does ok in vacuum
•will revisit when fresh gas is purchased
Some mods turn out better than others. For example, turns out hogging the venturis out as large as I did (25.6mm) introduces a very small glitch right above idle that, so far, I've not been able to get rid of*. However I think it's partially due to the low fuel level in the float bowls from today. Just below half way, while running at only 2psi. I'll adjust fuel pressure up tomorrow or the next time I get paid (to go get gas lol) and have some Nikki tuning time, to see if the glitch goes away.† Something tells me it will, but there might always be a narrow flat spot at about 1500 just due to the combination of parts in this setup (manifold, engine porting, air bleeds etc), as other setups don't exhibit this exact behavior. Every car is different.
*When I turn off the fuel pump to run the carb out of gas, which takes about a minute or so, this off idle glitch gets really wide and encompasses most of the rev range. We're talking from right above idle to like 4 or 5 grand and then it smooths out. It's just a faster way to run the carb out of gas before you take the top off for jet changes etc. I'm not sure that this is really the right way to do it, but I feel it's better than having to use a turkey baster or to just flip the carb upside down above an oil drain pan or some other container to get the gas out. The point is the very small glitch this carb has now wasn't noticed very much until it started running at about 2psi with a lower float level, and I'm sure my large venturis have something to do with it. In other words, the lower the float bowl level, the wider the glitch. It could have something to do with the amount of holes in the emulsion tubes as well.
†I nearly ran out of gas while test driving today. This is why the fuel pressure crept down to just 2psi. You could see the gauge move every time a bubble would make its way through the mallory. Good thing my tank has a sump cup. It lets me run the tank way down to just about empty. I used to be able to hear when the fuel pump was sucking air bubbles but now that it is so quiet from the noise isolation mod I did, it makes it harder to tell. Oh well, a quiet fuel pump sure is nice.
Just today I made some tuning changes because it was too lean now with the larger venturis. We're talking 14 to 15 AFR cruise and lousy low end tip in. Also it's harder to start and the idle isn't as good. Not to mention the off idle glitch.
The carb had 90 primary air, drilled 118 primary fuel, drilled 118 secondary air, 150 secondary fuel. This combo worked ok at 24.9mm and 2.5 to 3psi.
Swapped to 70 primary air. This reduced the glitch and added some tip-in, but it was still running a bit lean at cruise. Also the secondaries have a very small hiccup when they open now. Man, I thought I was done with secondary tuning.
Swapped to 60 primary air and decided to try 106 secondary air. This woke up the low end tip-in quite well, but the off idle glitch was still there. It was still lean at cruise but a little bit better than with the 70s. Gotta swap in some bigger primary fuel jets next, I think. Also the secondaries had a weird stumble. Since I was getting super low on gas, I decided not to push my luck with boost so only tested in vacuum after this.
Next I swapped out the 118 primary fuel jets and swapped in some Holley air bleeds that are about 130 metric. Took it for a spin. Um, now it was too rich at cruise, like 11 to 12. The off idle glitch was nearly gone but the low fuel level in the bowls and the 2psi (due to basically running out of gas) prevented any more driving. But I think I got my answer. Maybe keep the current Holley 130s and just swap from 60s back to 70s, maybe?
Since my drilled 118s are actually closer to a factory 122 or so, I figured 125s are pretty close and might not profit me very much if I were to get a set, and since I don't have any 125s just lying around anyway, I decided to keep the Holley 130s in there, and just swap the primary air bleeds from 60 back up to 70. Also swapped the 106 secondaries back to 118. This did the trick!
I decided to risk driving it one more time just around the block and it paid off. The off idle glitch is nearly gone and the low end tip in is still good enough. The slightly larger air bleeds leaned out the cruise to 12 to 13 (and I saw a couple of 14s in there!) which I can live with for now, and it started pretty easy and the idle was able to be tuned back to 12.2 where the engine runs best.
In all, a productive day.
Cliff notes:
•70 pri air, 130 pri fuel, 118 sec air, 150 sec fuel
•ran low on gas and decided to not tune in boost
•does ok in vacuum
•will revisit when fresh gas is purchased
03-07-15, 09:39 PM
#96
carb whisperer
03-07-15, 10:00 PM
#97
That's where it seems to idle best whether warm or cold. Of course, being a Nikki, it always has a lean cold idle so I gotta keep it running with my foot. Something to do with a cast iron baseplate, steel shafts and some bushings that wear over time. The fact that iron doesn't change much dimensionally as it heats up, but steel does. So when the carb is cold, lots more air leaks in along the shafts, but not so much when the carb is all warmed up. Does that make sense?
Anyway the first day I installed the wideband, I let the engine tell me what it wanted, and adjusted the carb to suit. 12.2 or 12.3 was what the wideband was showing when the engine idled best, so I memorized the number and started tuning the idles of the other carbs to this number or close to it, and the engine consistantly liked it there.
The reason rotaries like a rich idle is due to the way they run at low RPM and the shape of the combustion chamber. I do what j9fd3s does. Just give it what it wants. Don't chase numbers on a wideband (unless you already know what your engine wants!).
Anyway the first day I installed the wideband, I let the engine tell me what it wanted, and adjusted the carb to suit. 12.2 or 12.3 was what the wideband was showing when the engine idled best, so I memorized the number and started tuning the idles of the other carbs to this number or close to it, and the engine consistantly liked it there.
The reason rotaries like a rich idle is due to the way they run at low RPM and the shape of the combustion chamber. I do what j9fd3s does. Just give it what it wants. Don't chase numbers on a wideband (unless you already know what your engine wants!).
03-07-15, 10:07 PM
#98
carb whisperer
That's where it seems to idle best whether warm or cold. Of course, being a Nikki, it always has a lean cold idle so I gotta keep it running with my foot. Something to do with a cast iron baseplate, steel shafts and some bushings that wear over time. The fact that iron doesn't change much dimensionally as it heats up, but steel does. So when the carb is cold, lots more air leaks in along the shafts, but not so much when the carb is all warmed up. Does that make sense?
Anyway the first day I installed the wideband, I let the engine tell me what it wanted, and adjusted the carb to suit. 12.2 or 12.3 was what the wideband was showing when the engine idled best, so I memorized the number and started tuning the idles of the other carbs to this number or close to it, and the engine consistantly liked it there.
The reason rotaries like a rich idle is due to the way they run at low RPM and the shape of the combustion chamber. I do what j9fd3s does. Just give it what it wants. Don't chase numbers on a wideband (unless you already know what your engine wants!).
Anyway the first day I installed the wideband, I let the engine tell me what it wanted, and adjusted the carb to suit. 12.2 or 12.3 was what the wideband was showing when the engine idled best, so I memorized the number and started tuning the idles of the other carbs to this number or close to it, and the engine consistantly liked it there.
The reason rotaries like a rich idle is due to the way they run at low RPM and the shape of the combustion chamber. I do what j9fd3s does. Just give it what it wants. Don't chase numbers on a wideband (unless you already know what your engine wants!).
I think mine gets more than it wants, based on the always dark spark plugs. But if I even go down 1 jet size it starts to surge at freeway speeds uphill.
My engine likes to be pig rich on tip in, and transition. Small slow air bleeds, big accel pump.
The thing that stinks is after I have it running nicely while driving, a blip of the throttle free revving is poor response and even misses badly. Sounds like it hits a rev limiter.
03-07-15, 10:12 PM
#99
Hmm, mine did that today. The weird ghost rev limiter that it's had before. One of the reasons to go to 70 air bleeds was to try to get rid of it. My other carb with the 80 air bleeds didn't have that issue, but did when it had 90s.
The off idle glitch is a lean flat spot. The wideband jumps to like 16 or leaner.
The off idle glitch is a lean flat spot. The wideband jumps to like 16 or leaner.
03-07-15, 10:16 PM
#100
Here is PercentSevenC's boosted weber that acted like it had a rev limiter too. He blamed ignition. Turned out to be partially true. Was a bad coil, wire and spark plug that would misfire. The ignitors were fine. The rest was carb related.
By the way, I got his Mallory and S5 turbo. Also that BOV you hear.
By the way, I got his Mallory and S5 turbo. Also that BOV you hear.