Boost prep a Nikki (how to)
03-17-15, 09:17 PM
#26
That is correct. But there is more to it. The other half of the equation is in using the long travel diaphragms in the hygrade kits. This mod isn't quite as effective if you use the original FB short travel diaphragms.
Quingdao, imagine cutting out more than just six gaskets for one carb. Try enough for two carbs and some spares for your next carb. That really sucked. I had to come up with a better solution.
Quingdao, imagine cutting out more than just six gaskets for one carb. Try enough for two carbs and some spares for your next carb. That really sucked. I had to come up with a better solution.
03-17-15, 09:19 PM
#27
I see. So the pump Just puts pressure on a volume of liquid. It doesn't actually move the amount in the cone that is the diaphragm. And it moves it at the rate of the orifice drilled in the accelerator pump jet.
I've only had a few carbs with accelerator pumps. Kinda new to the concept.
I've only had a few carbs with accelerator pumps. Kinda new to the concept.
03-17-15, 09:31 PM
#28
Sterling came up with this accel pump mod idea after studying Holley carbs and their different cc volumes and other available adjustments. I tend to give him credit every time I talk about.
I take full credit for the 118 drilled nickel plated 60s in the primary slow air bleed holes as a means to recalibrate an idle circuit for use with hogged venturis and it just so happens to work better with boost too. It is perhaps the only way to make it work right with boost. That one is all mine.
I take full credit for the 118 drilled nickel plated 60s in the primary slow air bleed holes as a means to recalibrate an idle circuit for use with hogged venturis and it just so happens to work better with boost too. It is perhaps the only way to make it work right with boost. That one is all mine.
03-18-15, 06:22 PM
#29
Jeff. Over a decade ago, i noticed that the 4309 has a fluctuating fuel pressure at idle and there were times when i was unable to reduce the pressure below 6psi (msd FI pump, independent fuel pump wiring). I got tired of it that i went back to a holley reg which i modified. What have you done to resolve this issue.
03-18-15, 09:48 PM
#30
Send details: GSL-SE tank, 1/2" hardline from tank to 3/8" reducer fitting, Fram G3 filter, inlet of MSD 2225 is 3/8", outlet is 5/16", 5/16" hardline under car, to Mallory with a brass Tee fitting also in 5/16" over to Nikki.
Return details: 3/8" from Mallory to a 3/8" hardline installed under car, reducer down to 5/16" to go up over diff and into the tank.
The Mallory can now drop down to 1psi on this new setup. The old setup could not go down past 2.5psi but sometimes would fluctuate from 2psi to 3psi. The old setup had a 3/8" send and a 5/16" return. As you know, this is wrong.
It was even worse when I had a walbro 255 in there. It couldn't drop below 5psi. But how would the walbro do now with correctly sized send and return lines? Don't know and don't care. The MSD pump is perfect.
Return details: 3/8" from Mallory to a 3/8" hardline installed under car, reducer down to 5/16" to go up over diff and into the tank.
The Mallory can now drop down to 1psi on this new setup.
The old setup could not go down past 2.5psi but sometimes would fluctuate from 2psi to 3psi. The old setup had a 3/8" send and a 5/16" return. As you know, this is wrong.It was even worse when I had a walbro 255 in there. It couldn't drop below 5psi. But how would the walbro do now with correctly sized send and return lines? Don't know and don't care. The MSD pump is perfect.
Last edited by Jeff20B; 03-18-15 at 10:13 PM.
03-18-15, 10:51 PM
#31
I have the Walbro GSL392 and a 5/16" return. I have military grade resistors that drop the voltage going to the pump down to about 9v, and I still can't keep it under 4 PSI. I still have the stock return line on the carb so it handles it, but barely. Wouldn't recommend that pump for any carb setup.
03-18-15, 11:12 PM
#32
I just got my AN-6 line in today for a return line. I shouldn't have any issues. Or at least that's what I'm hoping.
I'm gonna make the AN-6 return strait into the tank. No bottlenecks.
If this runs fine I won't do anything further, but if I run into a starvation issue I'll braze in a 1/2" solid line from the tank to the pump.
I'm gonna make the AN-6 return strait into the tank. No bottlenecks.
If this runs fine I won't do anything further, but if I run into a starvation issue I'll braze in a 1/2" solid line from the tank to the pump.
03-19-15, 07:46 AM
#33
carb whisperer
Yeah, the MSD 2225 and the Weber Redline pump I ran last summer are very similar. The factory 1/4 (6mm) return line was too small for the high pressure. I believe that to be true for any fuel pump over 15 psi... 5/16 (8mm) and 3/8 (10mm) line are recommended for high pressure returns by most performance shops.
the GSLSE has 8mm send AND return and should work well until youre getting into pressurized carbs like jeff did. the 3/8 would help relieve any pressure on the seat of the regulator
the GSLSE has 8mm send AND return and should work well until youre getting into pressurized carbs like jeff did. the 3/8 would help relieve any pressure on the seat of the regulator
03-19-15, 10:06 AM
#34
Yeah I wasn't sure how it would turn out but it seems to have worked great with the 3/8" return under the car leading into the GSL-SE 5/16" return line into the tank. It's not to the letter of the instructions, but the Mallory is able to get 1psi. It is good and a lot less flood prone than before. The carb I'm using right now used to want to flood any time it saw anything above atmospheric, and now it runs in boost beautifully.
This is similar to PercentSevenC's succesful setup on his '83 where we did a 5/16" hardline under the car and then it contracts down to 1/4" where it leads into the tank. At the time we didn't know it shiuld have been 3/8" all the way back but he said his could go down to 1psi.
This is similar to PercentSevenC's succesful setup on his '83 where we did a 5/16" hardline under the car and then it contracts down to 1/4" where it leads into the tank. At the time we didn't know it shiuld have been 3/8" all the way back but he said his could go down to 1psi.
03-19-15, 04:23 PM
#36
Speaking of "runs in boost beautifully" I just did a quick jet and air bleed change in this carb with the almost oversized for a 74 ported 13B, 25.4mm venturis Nikki:
primary fuel jets: drilled 118 (used to have factory 130)
primary air bleeds: 70
secondary fuel jets: 155
secondary air bleeds: aftermarket MZTX 105 (used to have drilled 118)
As you can see I swapped in smaller fuel jets in the primaries and smaller air bleeds in the secondaries. I did this because the carb was too rich at part throttle cruise (was 11 on the wideband), and the secondaries still had a small bog/delay/hiccup when they'd open. About 1/4 second. Good, but could be better. They also ran at 11.3 to 11.7 in boost, so the whole carb was pretty good, but I knew I could make it better.
The new tune is only slightly more glitchy when cold due to the slightly leaner primaries, but then all carbs like this tend to run lean when cold so it's a barely noticeable difference. A fair tradeoff for better gas mileage, and still great AFRs in boost. When warmed up, it runs the same as before. In other words, basically perfect.
The results are a part throttle cruise at around 13 now instead of 11, so better gas mileage without hurting the idle quality or driveability, and the secondary delay is basically gone with the 105s from Mazdatrix swapped in the modded secondary main air bleeds. When I say basically gone, I mean you punch it and less than one tenth of one second later, the secondaries kick in. As you can imagine, this is such a short delay that it's virtually unoticeable.
I'm not done tuning yet. I still have a set of factory 100 jets I could try in the secondary main air bleeds next, but I'm going to follow Yaw's tuning advice and give it a day or two before I swap them in, if I even bother. Like I said the classic Nikki secondary hiccup is so short now, most drivers wouldn't even notice it. Only I do because I've worked steadily to reduce it from an original 2 seconds all the way down to nothing, which is where it's basically at. Seriously. I honestly could live with it as-is right now. It's that good.
Oh and the AFRs in boost start out at 11 right when you puch it, and then as the turbo spools up and boost starts to build, the Mallory responds and raises fuel pressure which brings the AFRs to 10.0 as the rear wheels broke loose in 3rd gear going up my test hill.
As you know, 10.0 is kinda rich, even with boost, so I could swap from the current 155s down to 150s if I really wanted to. However I like seeing 11 when I first punch it, for safety, so still debating it.
I wonder what bad 83 or anyone else still adhering to the old tuning philosophies would say about such small secondary jets?
Anyway this is how you do a "boost tune" or this is how I do it, at least. It's good to keep a jet change journal until you get good enough at it that you don't need to write stuff down anymore. I still like to because I've got four boost prepped carbs here, each with unique jet & air bleed combinations, so it can get a little confusing sometimes.
Hope this gives you guys a feel for what the Nikki wants in general and helps your initial NA tunes. Remember a Nikki wants about ten numbers bigger fuel jets and maybe slightly bigger air bleeds for an NA tune. I'd say 130 primary fuel jets are a good place for you to start if you do the nickel plated 60s and stock 70 air bleeds, which is a must for an eventual boost tune but also works NA.
primary fuel jets: drilled 118 (used to have factory 130)
primary air bleeds: 70
secondary fuel jets: 155
secondary air bleeds: aftermarket MZTX 105 (used to have drilled 118)
As you can see I swapped in smaller fuel jets in the primaries and smaller air bleeds in the secondaries. I did this because the carb was too rich at part throttle cruise (was 11 on the wideband), and the secondaries still had a small bog/delay/hiccup when they'd open. About 1/4 second. Good, but could be better. They also ran at 11.3 to 11.7 in boost, so the whole carb was pretty good, but I knew I could make it better.
The new tune is only slightly more glitchy when cold due to the slightly leaner primaries, but then all carbs like this tend to run lean when cold so it's a barely noticeable difference. A fair tradeoff for better gas mileage, and still great AFRs in boost. When warmed up, it runs the same as before. In other words, basically perfect.
The results are a part throttle cruise at around 13 now instead of 11, so better gas mileage without hurting the idle quality or driveability, and the secondary delay is basically gone with the 105s from Mazdatrix swapped in the modded secondary main air bleeds. When I say basically gone, I mean you punch it and less than one tenth of one second later, the secondaries kick in. As you can imagine, this is such a short delay that it's virtually unoticeable.
I'm not done tuning yet.
I still have a set of factory 100 jets I could try in the secondary main air bleeds next, but I'm going to follow Yaw's tuning advice and give it a day or two before I swap them in, if I even bother. Like I said the classic Nikki secondary hiccup is so short now, most drivers wouldn't even notice it. Only I do because I've worked steadily to reduce it from an original 2 seconds all the way down to nothing, which is where it's basically at. Seriously. I honestly could live with it as-is right now. It's that good. Oh and the AFRs in boost start out at 11 right when you puch it, and then as the turbo spools up and boost starts to build, the Mallory responds and raises fuel pressure which brings the AFRs to 10.0 as the rear wheels broke loose in 3rd gear going up my test hill.
As you know, 10.0 is kinda rich, even with boost, so I could swap from the current 155s down to 150s if I really wanted to. However I like seeing 11 when I first punch it, for safety, so still debating it.
I wonder what bad 83 or anyone else still adhering to the old tuning philosophies would say about such small secondary jets?
Anyway this is how you do a "boost tune" or this is how I do it, at least. It's good to keep a jet change journal until you get good enough at it that you don't need to write stuff down anymore. I still like to because I've got four boost prepped carbs here, each with unique jet & air bleed combinations, so it can get a little confusing sometimes.
Hope this gives you guys a feel for what the Nikki wants in general and helps your initial NA tunes. Remember a Nikki wants about ten numbers bigger fuel jets and maybe slightly bigger air bleeds for an NA tune. I'd say 130 primary fuel jets are a good place for you to start if you do the nickel plated 60s and stock 70 air bleeds, which is a must for an eventual boost tune but also works NA.
03-21-15, 02:51 AM
#37
I spent some time today figuring out more boost tuning for the Nikkis. Yesterday's tune was good but the secondaries still had about a tenth of a second delay. And still kinda too rich so the answer is slightly smaller air bleeds and slightly smaller fuel jets in the secondary side. The primaries were fine so I can leave them alone.
The secondary parts were 155 jets and 105 air bleeds. I swapped in some 150 fuel jets but I have a couple of air bleed choices and I'd like your input.
I have 100, 94 and 92 to choose from.
Now consider how the previous tune ran when the secondary delay was about 1/4 second. It still had the 155 jets but the air bleeds were 118 that I drilled myself. With this tune, the wideband was 11.3 to 11.7, so just about perfect for boost. Only issue was the quarter second delay that going to 105 air bleeds was supposed to fix, which it almost perfectly did, but then the AFRs got richer at 10.0. That is why I swapped in the 150 fuel jets today, to compensate for smaller air bleeds.
Now that the 150 jets are in, it should lean out the AFRs to probably back to 11 again. But I want to make sure the delay is gone for good! So again the question comes back to the air bleeds: 100, 94 or 92.
Now consider how the air bleed change from 118 to 105 caused the delay to shorten from one quarter second to one tenth second. That was a reduction of only 13 numbers. These 13 numbers made a pretty big difference. Now consider how going from 105 to 92 is also 13 numbers and you start to see a pattern.
See, I'm starting to think the 100s are too close to 105 to make much difference. Same how 94 is too close to 92 to be noticeable. So I'm considering going from 105 straight to 92 to see what will happen, but my old world tuning philosophy keeps coming back that says the secondary air bleeds need to be kinda big blah blah blah. To put it another way, I'm worried because in my mind, 90ish air bleeds are way too small for the secondaries based on all the NA tuning I've seen. Heck the SA carbs came with 90 primary air bleeds and some carbs came with 160 secondary air bleeds stock! This is a drastic change of up to 68 numbers! And yet my common sense returns and reminds me of the excellent results I've had with reducing the air bleeds everywhere else in the carb for boost because there is always plenty of air with a turbo so less need for all these air bleeds everywhere. Does that make sense?
There's also varying carb conditions like temperature, load etc that I've observed can take the orignal 1/4 second delay and either increase it to 1/2 second under some conditions or reduce it to nothing under other conditions. My goal as a carb tuner is to account for the times when the carb is likely to want to have a 1/2 second delay and reduce it to zero as much as I can, otherwise, well, you know. People complain.
The 1/2 second thing was just an example. More realistically the tenth of a second delay could get longer under some conditions, so if I can over-compensate for it, by reducing the secondary air bleeds beyond where I think they'd work best, ideally 100, and make them smaller than that in order to cover most if not all driving conditions, while not getting too pig-rich in the process, it makes sense to drop them down by another few numbers until I'm sure it'll work every time. If that means going to 92s, then so be it. It's a one size fits all approach but then I think a factory tune is like that.
I gotta say I'm a bit concerned that 92 will be way too small, but then the idle circuit primary slow bleeds benefited going from 170 down to 118. That's a change of 52 numbers. Heck my secondary slow air bleeds went from 60 to 0 and the main air bleeds went from 140 to 105 already. Together that's a change of 95 numbers! So what's another 13, right?
What if I need 145 or even 140 fuel jets after this? Not even I have the stomach for that. Let's hope it doesn't come to that. 150 sounds like a safe bet for now, and it used to read 12 on the wideband back when the secondary slow and main bleeds were still stock, so some progress has been made if they read 10.something now. Thoughts?
The secondary parts were 155 jets and 105 air bleeds. I swapped in some 150 fuel jets but I have a couple of air bleed choices and I'd like your input.
I have 100, 94 and 92 to choose from.
Now consider how the previous tune ran when the secondary delay was about 1/4 second. It still had the 155 jets but the air bleeds were 118 that I drilled myself. With this tune, the wideband was 11.3 to 11.7, so just about perfect for boost. Only issue was the quarter second delay that going to 105 air bleeds was supposed to fix, which it almost perfectly did, but then the AFRs got richer at 10.0. That is why I swapped in the 150 fuel jets today, to compensate for smaller air bleeds.
Now that the 150 jets are in, it should lean out the AFRs to probably back to 11 again. But I want to make sure the delay is gone for good! So again the question comes back to the air bleeds: 100, 94 or 92.
Now consider how the air bleed change from 118 to 105 caused the delay to shorten from one quarter second to one tenth second. That was a reduction of only 13 numbers. These 13 numbers made a pretty big difference. Now consider how going from 105 to 92 is also 13 numbers and you start to see a pattern.
See, I'm starting to think the 100s are too close to 105 to make much difference. Same how 94 is too close to 92 to be noticeable. So I'm considering going from 105 straight to 92 to see what will happen, but my old world tuning philosophy keeps coming back that says the secondary air bleeds need to be kinda big blah blah blah. To put it another way, I'm worried because in my mind, 90ish air bleeds are way too small for the secondaries based on all the NA tuning I've seen. Heck the SA carbs came with 90 primary air bleeds and some carbs came with 160 secondary air bleeds stock! This is a drastic change of up to 68 numbers! And yet my common sense returns and reminds me of the excellent results I've had with reducing the air bleeds everywhere else in the carb for boost because there is always plenty of air with a turbo so less need for all these air bleeds everywhere. Does that make sense?
There's also varying carb conditions like temperature, load etc that I've observed can take the orignal 1/4 second delay and either increase it to 1/2 second under some conditions or reduce it to nothing under other conditions. My goal as a carb tuner is to account for the times when the carb is likely to want to have a 1/2 second delay and reduce it to zero as much as I can, otherwise, well, you know. People complain.
The 1/2 second thing was just an example. More realistically the tenth of a second delay could get longer under some conditions, so if I can over-compensate for it, by reducing the secondary air bleeds beyond where I think they'd work best, ideally 100, and make them smaller than that in order to cover most if not all driving conditions, while not getting too pig-rich in the process, it makes sense to drop them down by another few numbers until I'm sure it'll work every time. If that means going to 92s, then so be it. It's a one size fits all approach but then I think a factory tune is like that.
I gotta say I'm a bit concerned that 92 will be way too small, but then the idle circuit primary slow bleeds benefited going from 170 down to 118. That's a change of 52 numbers. Heck my secondary slow air bleeds went from 60 to 0 and the main air bleeds went from 140 to 105 already. Together that's a change of 95 numbers! So what's another 13, right?
What if I need 145 or even 140 fuel jets after this? Not even I have the stomach for that. Let's hope it doesn't come to that. 150 sounds like a safe bet for now, and it used to read 12 on the wideband back when the secondary slow and main bleeds were still stock, so some progress has been made if they read 10.something now. Thoughts?
03-21-15, 04:44 PM
#38
carb whisperer
Id just go small until the bog is gone, then jet it like a clean slate. The bog is the fuel not coming on soon enough to cover the gap.
You should maybe try something else ill bet you didnt think of.
If you REDUCE the size of your pump nozzle a little bit, youll lengthen the duration of the shot a little bit. And at 1/10th of a second of delay, youre 90% covered for the transition.
The slightly smaller nozzle might extend the duration (not volume) of the shot just a little longer to cover it.
I tuned my 465's this way. I used extremely small nozzles with already fat transition circuits (which you have) to lengthen my pump shot far enough to get a nice and crispy secondary response even with the lightest holley spring (white).
Until now I kept that a secret, hope it helps.
PS: EDIT BUTTON OMG
You should maybe try something else ill bet you didnt think of.
If you REDUCE the size of your pump nozzle a little bit, youll lengthen the duration of the shot a little bit. And at 1/10th of a second of delay, youre 90% covered for the transition.
The slightly smaller nozzle might extend the duration (not volume) of the shot just a little longer to cover it.
I tuned my 465's this way. I used extremely small nozzles with already fat transition circuits (which you have) to lengthen my pump shot far enough to get a nice and crispy secondary response even with the lightest holley spring (white).
Until now I kept that a secret, hope it helps.
PS: EDIT BUTTON OMG
Last edited by wankel=awesome; 03-21-15 at 04:45 PM. Reason: because i can
03-22-15, 01:37 AM
#39
I like that idea. I might have inadvertantly stumbled onto it on one of the carbs today but not the other. Let me explain.
The first carb no longer has a secondary bog! I must have found the right combo of tuning parts because when you punch it, there is no longer a delay. It instantly throws you back in the seat like a proper mech secondary mod is supposed to, only it does it with boost.
25.4mm carb:
pri air: 70
pri fuel: drilled 118
sec air: 100
sec fuel: 150
The primary circuit is a little on the lean side, so I think a set of 125s should put this carb at 100% tuned!
I won't bore you with the details of how I got here, only to say I tested some factory 130 jets and it was too rich, and the current drilled 118s are a a bit too lean, so the conclusion is 125.
Now the other carb is the one that's giving me all kinds of trouble. Its first tune was:
25.6mm carb:
pri air: 60
pri fuel: drilled 118
sec air: 94
sec fuel: 150
And this didn't want to run very well. It still had the off idle lean spot at 1500 which the 60 air bleeds were supposed to help with (they didn't), but would also glitch above 2000 now. And the primary circuit at part throttle cruise would run at 13 on the wideband but just poorly overall. I could tell the engine didn't like this tune. What's worse is the secondaries had about a 1/2 second delay, even with little 94 jets in the secondary air bleeds! Uhg!
My first tuning changes consisted of swapping from drilled 118 to factory 130 jets. Result: Still had a poor running primary circuit but wasn't as lean (actually kinda rich now) and the secondaries still had a delay! I think this time it was consistantly 1/4 second. The AFR was 11 to 10 the whole time. Tested in 1st 2nd and 3rd. Same delay each time. Uhg!
Next tuning changes consisted of swapping in some 70 primary air bleeds and some 91 jets into the secondary air bleeds. Left the fuel jets alone. Result: Much better primary drivability but the 1500 lean spot is still there. The only way to get rid of it now is to just swap in smaller venturis. Oh well. Not going to do it right away because while driving with this current tune, it's hard to notice the actual glitch as the accel pump covers for it. You only really notice it when you slowly idle it up to 1500. This never really occurs when you're driving so that's why it took me a while to notice.
Speaking of accel pump and tip in, it's very strong with this carb. The other carb feels soft compared to this one. What the other carb does with finesse, this carb does with brute force. It's a much more severe carb than any of the others, this 25.6mm carb. Hmm, it just might make a great carb for the REPU after all. Or I might leave it here in the 7 as it does pretty well I must say. Feels about 80% tuned at this point.
But the secondary bog is still there! Less so than before, though. Like 1/8 to 1/4 second but it depends on load such as the way it's being driven up a hill. Seems more load dependant than you;d think it should be. Still might make a good carb for the REPU.
Current tune:
pri air: 70
pri fuel: factory 130
sec air: 91
sec fuel: 150
wankel=awesome, so you're saying I need to reduce the secondary air bleeds even smaller until the bog is gone? Then rejet like a clean slate?
Hmm, I don't have any jets smaller than 91 here. Now I'm wondering what it would be like to swap in jets blocked with solder. At this point, what have I got to lose? Seems like this carb has some unmetered air leaking in from somewhere. Probably the shafts.
By the way I don't think the accel pump is the issue on this carb but I can swap in a stock drilled nozzle as my current one is drilled to 118.
The first carb no longer has a secondary bog! I must have found the right combo of tuning parts because when you punch it, there is no longer a delay.
It instantly throws you back in the seat like a proper mech secondary mod is supposed to, only it does it with boost.25.4mm carb:
pri air: 70
pri fuel: drilled 118
sec air: 100
sec fuel: 150
The primary circuit is a little on the lean side, so I think a set of 125s should put this carb at 100% tuned!
I won't bore you with the details of how I got here, only to say I tested some factory 130 jets and it was too rich, and the current drilled 118s are a a bit too lean, so the conclusion is 125.
Now the other carb is the one that's giving me all kinds of trouble. Its first tune was:
25.6mm carb:
pri air: 60
pri fuel: drilled 118
sec air: 94
sec fuel: 150
And this didn't want to run very well. It still had the off idle lean spot at 1500 which the 60 air bleeds were supposed to help with (they didn't), but would also glitch above 2000 now. And the primary circuit at part throttle cruise would run at 13 on the wideband but just poorly overall. I could tell the engine didn't like this tune. What's worse is the secondaries had about a 1/2 second delay, even with little 94 jets in the secondary air bleeds! Uhg!
My first tuning changes consisted of swapping from drilled 118 to factory 130 jets. Result: Still had a poor running primary circuit but wasn't as lean (actually kinda rich now) and the secondaries still had a delay! I think this time it was consistantly 1/4 second. The AFR was 11 to 10 the whole time. Tested in 1st 2nd and 3rd. Same delay each time. Uhg!
Next tuning changes consisted of swapping in some 70 primary air bleeds and some 91 jets into the secondary air bleeds. Left the fuel jets alone. Result: Much better primary drivability but the 1500 lean spot is still there. The only way to get rid of it now is to just swap in smaller venturis. Oh well. Not going to do it right away because while driving with this current tune, it's hard to notice the actual glitch as the accel pump covers for it. You only really notice it when you slowly idle it up to 1500. This never really occurs when you're driving so that's why it took me a while to notice.
Speaking of accel pump and tip in, it's very strong with this carb. The other carb feels soft compared to this one. What the other carb does with finesse, this carb does with brute force. It's a much more severe carb than any of the others, this 25.6mm carb. Hmm, it just might make a great carb for the REPU after all. Or I might leave it here in the 7 as it does pretty well I must say. Feels about 80% tuned at this point.
But the secondary bog is still there! Less so than before, though. Like 1/8 to 1/4 second but it depends on load such as the way it's being driven up a hill. Seems more load dependant than you;d think it should be. Still might make a good carb for the REPU.
Current tune:
pri air: 70
pri fuel: factory 130
sec air: 91
sec fuel: 150
wankel=awesome, so you're saying I need to reduce the secondary air bleeds even smaller until the bog is gone? Then rejet like a clean slate?
Hmm, I don't have any jets smaller than 91 here. Now I'm wondering what it would be like to swap in jets blocked with solder.
At this point, what have I got to lose? Seems like this carb has some unmetered air leaking in from somewhere. Probably the shafts.By the way I don't think the accel pump is the issue on this carb but I can swap in a stock drilled nozzle as my current one is drilled to 118.
03-22-15, 05:26 PM
#41
Ok, cool. Thanks for the info.
And as usual, something you said clicked and now I have a new course of action to try. You said you have fat transition circuits. What if I made mine even fatter? I ask because I think mine aren't lasting long enough.
The one set of slow air bleeds I've never messed with is the long primary one with the 46 stamp. I looked and it turns out I have a set of 50 and 42. You can see where I'm going with this.
I also looked through my little brass Hitachi air bleeds, the type that are similar to the short ones used in a Nikki. The assortment consists of 60, 80, 90 100 and the rest are 160. These are used as main air bleeds in Hitachis and are really convenient to play with. They only need a little modding to fit in a Nikki.
The most important part is they are smaller than my 118 drill bit! This means I can now tune my idle circuit and transition circuit to hopefully get rid of the 1500 glitch.
Think it'll help when the secondaries open, too?
This may be related: What I understand about tuning a weber, which is next to nothing, is what everyone always talks about where they need to tune the idle circuit to keep it going longer into the mains even as the mains are coming online, to avoid a transition flat spot. Is that right?
So why can't I do that with the Nikki? It seems my idle circuit only covers up to 1500 RPM when the venturis are this large, which is too low for the primaries to be online yet, but too high for the idle circuit.
Should I swap in the 100s and the 42s and see what I get?
And as usual, something you said clicked and now I have a new course of action to try. You said you have fat transition circuits. What if I made mine even fatter? I ask because I think mine aren't lasting long enough.
The one set of slow air bleeds I've never messed with is the long primary one with the 46 stamp. I looked and it turns out I have a set of 50 and 42. You can see where I'm going with this.
I also looked through my little brass Hitachi air bleeds, the type that are similar to the short ones used in a Nikki. The assortment consists of 60, 80, 90 100 and the rest are 160. These are used as main air bleeds in Hitachis and are really convenient to play with. They only need a little modding to fit in a Nikki.
The most important part is they are smaller than my 118 drill bit! This means I can now tune my idle circuit and transition circuit to hopefully get rid of the 1500 glitch.
Think it'll help when the secondaries open, too?
This may be related: What I understand about tuning a weber, which is next to nothing, is what everyone always talks about where they need to tune the idle circuit to keep it going longer into the mains even as the mains are coming online, to avoid a transition flat spot. Is that right?
So why can't I do that with the Nikki? It seems my idle circuit only covers up to 1500 RPM when the venturis are this large, which is too low for the primaries to be online yet, but too high for the idle circuit.
Should I swap in the 100s and the 42s and see what I get?
03-22-15, 08:45 PM
#42
I have some good related news. A guy brought his stripped but stock FB carb over and I looked inside to make sure stuff was ok. Noticed the 170 slows there abd was like oh boy. I doubt this will work, but whatever.
I was right. The carb just didn't want to idle so I had to crank the mixture screw out pretty far and crank up the throttle stop screw. Still wanted to die a few seconds after a quick rev shot from the accel pump.
You know the answer by now. The stock 170s gotta go.
Took the top back off and was just about to swap in a set of SA 150s when I suddenly realized I was curious how some 118 drilled nickel plated 60s would do in an otherwise stock jetted and venturied carb. They work in all the other hogged out carbs I've tried them in so far. Why couldn't they work here?
See, the PO removed the choke flap and shaft. Without the choke to cause the carb to pull a stronger vacuum and thus richen up the cold idle, this carb would never idle well for the guy while cold and might still have issues when warm.
The result: Success! It fired up fast and idled just about perfect within a second or two. 100% improvement. I needed to crank the mixture screw way back in and let out the throttle stop screw a bit too. Got it to idle wherever I wanted it to at whatever AFR I wanted it at. But I settled on 950 to 1000 and 12.2 because my engine likes it best.
I mention this because it's kinda related to my boost prepped carbs. There has to be a way to make the 1500 lean spot carb work with some primary slow air bleed adjustments. But not sure if going smaller is the way to go. Something tells me it is but would like a second opinion before I dig in. Anyone?
I was right. The carb just didn't want to idle so I had to crank the mixture screw out pretty far and crank up the throttle stop screw. Still wanted to die a few seconds after a quick rev shot from the accel pump.
You know the answer by now. The stock 170s gotta go.
Took the top back off and was just about to swap in a set of SA 150s when I suddenly realized I was curious how some 118 drilled nickel plated 60s would do in an otherwise stock jetted and venturied carb. They work in all the other hogged out carbs I've tried them in so far. Why couldn't they work here?
See, the PO removed the choke flap and shaft. Without the choke to cause the carb to pull a stronger vacuum and thus richen up the cold idle, this carb would never idle well for the guy while cold and might still have issues when warm.
The result: Success! It fired up fast and idled just about perfect within a second or two. 100% improvement. I needed to crank the mixture screw way back in and let out the throttle stop screw a bit too. Got it to idle wherever I wanted it to at whatever AFR I wanted it at. But I settled on 950 to 1000 and 12.2 because my engine likes it best.
I mention this because it's kinda related to my boost prepped carbs. There has to be a way to make the 1500 lean spot carb work with some primary slow air bleed adjustments. But not sure if going smaller is the way to go. Something tells me it is but would like a second opinion before I dig in. Anyone?
03-22-15, 09:19 PM
#43
Just a quick list for tuning a 24mm venturi carb for boost:
Primary side:
120 primary fuel jets or drilled 118
70 primary main air bleeds
nickel plated 60s from the secondary side and drill them to 118 (.045") then swap them to the primary side
Leave the long slow air bleeds alone
Secondary side
150 secondary fuel jets
modded secondary main air bleeds to accept drilled 118 jets or 45 air bleeds
fill the brass primary slow air bleeds with solder and swap into secondary holes
fill the long sec slow bleeds with solder as well
Sound good? If you mod your carb the way I do, this should put you into the 80% tuned ballpark right out of the box. I wish I would have known half this stuff a year ago.
Primary side:
120 primary fuel jets or drilled 118
70 primary main air bleeds
nickel plated 60s from the secondary side and drill them to 118 (.045") then swap them to the primary side
Leave the long slow air bleeds alone
Secondary side
150 secondary fuel jets
modded secondary main air bleeds to accept drilled 118 jets or 45 air bleeds
fill the brass primary slow air bleeds with solder and swap into secondary holes
fill the long sec slow bleeds with solder as well
Sound good? If you mod your carb the way I do, this should put you into the 80% tuned ballpark right out of the box. I wish I would have known half this stuff a year ago.
But you loose me on the secondary side. You block off the slow air bleeds with solder? So, no air movement at all?
03-22-15, 09:29 PM
#44
carb whisperer
I have some good related news. A guy brought his stripped but stock FB carb over and I looked inside to make sure stuff was ok. Noticed the 170 slows there abd was like oh boy. I doubt this will work, but whatever.
I was right. The carb just didn't want to idle so I had to crank the mixture screw out pretty far and crank up the throttle stop screw. Still wanted to die a few seconds after a quick rev shot from the accel pump.
You know the answer by now. The stock 170s gotta go.
Took the top back off and was just about to swap in a set of SA 150s when I suddenly realized I was curious how some 118 drilled nickel plated 60s would do in an otherwise stock jetted and venturied carb. They work in all the other hogged out carbs I've tried them in so far. Why couldn't they work here?
See, the PO removed the choke flap and shaft. Without the choke to cause the carb to pull a stronger vacuum and thus richen up the cold idle, this carb would never idle well for the guy while cold and might still have issues when warm.
The result: Success! It fired up fast and idled just about perfect within a second or two. 100% improvement. I needed to crank the mixture screw way back in and let out the throttle stop screw a bit too. Got it to idle wherever I wanted it to at whatever AFR I wanted it at. But I settled on 950 to 1000 and 12.2 because my engine likes it best.
I mention this because it's kinda related to my boost prepped carbs. There has to be a way to make the 1500 lean spot carb work with some primary slow air bleed adjustments. But not sure if going smaller is the way to go. Something tells me it is but would like a second opinion before I dig in. Anyone?
I was right. The carb just didn't want to idle so I had to crank the mixture screw out pretty far and crank up the throttle stop screw. Still wanted to die a few seconds after a quick rev shot from the accel pump.
You know the answer by now. The stock 170s gotta go.
Took the top back off and was just about to swap in a set of SA 150s when I suddenly realized I was curious how some 118 drilled nickel plated 60s would do in an otherwise stock jetted and venturied carb. They work in all the other hogged out carbs I've tried them in so far. Why couldn't they work here?
See, the PO removed the choke flap and shaft. Without the choke to cause the carb to pull a stronger vacuum and thus richen up the cold idle, this carb would never idle well for the guy while cold and might still have issues when warm.
The result: Success! It fired up fast and idled just about perfect within a second or two. 100% improvement. I needed to crank the mixture screw way back in and let out the throttle stop screw a bit too. Got it to idle wherever I wanted it to at whatever AFR I wanted it at. But I settled on 950 to 1000 and 12.2 because my engine likes it best.
I mention this because it's kinda related to my boost prepped carbs. There has to be a way to make the 1500 lean spot carb work with some primary slow air bleed adjustments. But not sure if going smaller is the way to go. Something tells me it is but would like a second opinion before I dig in. Anyone?
03-22-15, 10:19 PM
#45
wankel=awesome thanks! Ok it is as simple as I hoped. Cool!
I already grabbed the 42 long slows and a set of 90s and tossed them in. I'll test this combo tomorrow.
Quingdao, you only block them off if you experience a secondary delay or bog, which if you're boosting, you wil. Fill the primary 150 through 190 short bleeds with solder and install in the secondary holes. Next fill the secondary long slow bleeds with solder and install. This can get tricky as the solder likes to flow out. I guess if you have some flux it'd be a good idea to use.
I already grabbed the 42 long slows and a set of 90s and tossed them in. I'll test this combo tomorrow.
Quingdao, you only block them off if you experience a secondary delay or bog, which if you're boosting, you wil. Fill the primary 150 through 190 short bleeds with solder and install in the secondary holes. Next fill the secondary long slow bleeds with solder and install. This can get tricky as the solder likes to flow out. I guess if you have some flux it'd be a good idea to use.
03-23-15, 04:02 AM
#46
Lolicon*** of RX-7 World
I'm really loving all this Info I really and I mean really can't wait to start finding another nikki so I can really do some testing for now I think I will keep stock so I can drive the car already have dibs on another engine with carb
03-23-15, 06:00 AM
#47
carb whisperer
Another trick is to tap a ball of lead shot into the orifice of the stock jet. Make sure you use the right size, and get it nice and tight. Then drill flattened lead plug for the smaller restriction you want. Since the lead is so soft, its easily worked with and easy to remove.
I do this instead of the solder! Much easier to drill through with tiny bits.
I do this instead of the solder! Much easier to drill through with tiny bits.
03-24-15, 12:53 PM
#48
Nice idea. I don't have any lead shot around though.
In my quest for inbetween sizes to get a Nikki tuned 100%, I started looking for 122 in a size and thread pitch that would fit and not interfere with anything. Wouldn't you know it, the lowly Weber jets in the 73801 style were the answer. Not from Mazdatrix, but from piercemanifolds. About half price too. But then what if I needed a size they don't list? I found another webpage that has some other sizes. Together we have virtually the entire range from 80 to 240 including inbetween sizes like 107, 117, 127, 137, 147 etc.
For 85, 95, 147, click Weber by Number | Carbs Unlimited
copy and past into search bar
73801.085
73801.095
73801.147
For 107, click Weber 32/36 DGV DGEV DGAV Parts Page scroll down to "DGEV Calibrated Parts" find "Main Jets", use drop down menu to find 107
For 117, 122, 127, 137, click MAIN JETS <br><font color="red">73801</font> and choose from the drop down menu.
Virtually every other size is mirrored across both websites.
Now you may be wondering why bother with any inbetween sizes at all? Isn't it all about testing different sizes until you find the one that makes the engine run best? But then why do others like Sterling not sweat the inbetween stuff and even recommend against it? Does that automatically mean inbetween sizes are not necessary? What are you, crazy? Sterling only did things the way he did them because he was following Yaw's lead in using Holley air bleeds which only offer close sizes, but not all that exact. And he admitted he had no jetting data what so ever about boost prepping these carbs, so take that with whatever degree of authority you want.
If I got a pack of Holley 49s, it would put me pretty close but the actual size I'm looking for is 48 which doesn't exist while 47 is too small. Seems Holley does every odd number. Plus I've noticed their stamps are not very deep. Basically poor quality control. And when you're getting into tuning as much as I am now, you come to appreciate the little things like a deeper easier to read stamp, and keeping things metric because the carbs are metric. I feel Sterling did us a disservice by going standard on all his listed air bleed and jet sizes because I can't know what it is at just a glance. I have to punch the numbers into an internet convertor which is really inconvenient. But I do understand the economics of his decision as the Holley air bleeds are a lot cheaper than even these $4.20 weber jets.
I recommend getting inbetween sizes because this thread is all about boost prepping and hogging the venturis. Such acts require very different jets and air bleeds from stock. And I wasn't interested in keeping track of a bunch of custom drilled jets with no real way to distinguish different sizes from one another, other than to poke a probe of a certain size in each one (using a drill bit or a needle gauge = too much work, plus the tedious drilling etc). Even though buying these jets at about 4 bucks a pop is more expensive in the end than a pack of tiny drill bits, or even Holley air bleeds, I like seeing what size it is by looking at the stamp on the side of the head. Tiny drill bits are nice and I'll get a set, but so far I haven't needed them as my 118 or .0465" drill bit has been a one size fits all solution. However I find the deeper into these carbs I dig, the more I need other sizes.
In my quest for inbetween sizes to get a Nikki tuned 100%, I started looking for 122 in a size and thread pitch that would fit and not interfere with anything. Wouldn't you know it, the lowly Weber jets in the 73801 style were the answer. Not from Mazdatrix, but from piercemanifolds. About half price too.
But then what if I needed a size they don't list? I found another webpage that has some other sizes. Together we have virtually the entire range from 80 to 240 including inbetween sizes like 107, 117, 127, 137, 147 etc.For 85, 95, 147, click Weber by Number | Carbs Unlimited
copy and past into search bar
73801.085
73801.095
73801.147
For 107, click Weber 32/36 DGV DGEV DGAV Parts Page scroll down to "DGEV Calibrated Parts" find "Main Jets", use drop down menu to find 107
For 117, 122, 127, 137, click MAIN JETS <br><font color="red">73801</font> and choose from the drop down menu.
Virtually every other size is mirrored across both websites.
Now you may be wondering why bother with any inbetween sizes at all? Isn't it all about testing different sizes until you find the one that makes the engine run best? But then why do others like Sterling not sweat the inbetween stuff and even recommend against it? Does that automatically mean inbetween sizes are not necessary? What are you, crazy? Sterling only did things the way he did them because he was following Yaw's lead in using Holley air bleeds which only offer close sizes, but not all that exact. And he admitted he had no jetting data what so ever about boost prepping these carbs, so take that with whatever degree of authority you want.
If I got a pack of Holley 49s, it would put me pretty close but the actual size I'm looking for is 48 which doesn't exist while 47 is too small. Seems Holley does every odd number. Plus I've noticed their stamps are not very deep. Basically poor quality control. And when you're getting into tuning as much as I am now, you come to appreciate the little things like a deeper easier to read stamp, and keeping things metric because the carbs are metric. I feel Sterling did us a disservice by going standard on all his listed air bleed and jet sizes because I can't know what it is at just a glance. I have to punch the numbers into an internet convertor which is really inconvenient. But I do understand the economics of his decision as the Holley air bleeds are a lot cheaper than even these $4.20 weber jets.
I recommend getting inbetween sizes because this thread is all about boost prepping and hogging the venturis. Such acts require very different jets and air bleeds from stock. And I wasn't interested in keeping track of a bunch of custom drilled jets with no real way to distinguish different sizes from one another, other than to poke a probe of a certain size in each one (using a drill bit or a needle gauge = too much work, plus the tedious drilling etc). Even though buying these jets at about 4 bucks a pop is more expensive in the end than a pack of tiny drill bits, or even Holley air bleeds, I like seeing what size it is by looking at the stamp on the side of the head. Tiny drill bits are nice and I'll get a set, but so far I haven't needed them as my 118 or .0465" drill bit has been a one size fits all solution. However I find the deeper into these carbs I dig, the more I need other sizes.
03-24-15, 07:02 PM
#49
Have you ever tried keihin jets? Or Motorcyclecarb.com? I don't know if they are still around; its been a while since I've tuned any motorbike carburetors.
But the advantage for bike carb jets is they are cheap as hell. They also offer different length and hole patterns on slow jets. and of course you can always cut them in half if they get in the way of the top.
http://www.ebay.com/itm/New-main-jets-for-Keihin-OKO-KOSO-PE-PWK-carburetor-carb-vergaser-choose-10-size-/221704840019?pt=Motorcycles_Parts_Accessories&hash=item339ea36353&vxp=mtr
EDIT: Mik jets are slimmer if I recall correctly.
But the advantage for bike carb jets is they are cheap as hell. They also offer different length and hole patterns on slow jets. and of course you can always cut them in half if they get in the way of the top.
http://www.ebay.com/itm/New-main-jets-for-Keihin-OKO-KOSO-PE-PWK-carburetor-carb-vergaser-choose-10-size-/221704840019?pt=Motorcycles_Parts_Accessories&hash=item339ea36353&vxp=mtr
EDIT: Mik jets are slimmer if I recall correctly.
Last edited by Qingdao; 03-24-15 at 07:07 PM.
03-24-15, 11:20 PM
#50
Those are really long. Where is the orifice? Is it down in the threaded section?
I just learned about Keihin jets yesterday. They have a different sizing scheme from everyone else. They'd fit the Nikki though, I'm pretty sure. But nah I'll likely get the weber jets. I know they fit the Nikki because I have a few already.
So I tested the 90 shorts and the 42 longs in the 25.6mm carb. It got rid of the 1500 lean spot! But it made the idle extremely rich so I had to turn the mixture screw all the way in to get back to 12.2, which would fluctuate to 11.9 and it made the engine vibrate. Obviously this isn't going to work. Interesting test though.
So I looked high and low for some 100 shorts but never found any. So I gave up and swapped the 118 drilled nickel plated 60s back in. The 1500 to 2000 lean spot came but but with less vengeance than before. I think the 42 longs are doing something. The mixture screw could also be backed out into its range again.
It seems the solution is to get a set of small drill bits and choose a size between 90 and 118, then drill a spare set of nickel plated 60s. Shouldn't be too hard. Somewhere mathematically in the middle around 105 or so should do it. Thoughts?
I just learned about Keihin jets yesterday. They have a different sizing scheme from everyone else. They'd fit the Nikki though, I'm pretty sure. But nah I'll likely get the weber jets. I know they fit the Nikki because I have a few already.
So I tested the 90 shorts and the 42 longs in the 25.6mm carb. It got rid of the 1500 lean spot! But it made the idle extremely rich so I had to turn the mixture screw all the way in to get back to 12.2, which would fluctuate to 11.9 and it made the engine vibrate. Obviously this isn't going to work. Interesting test though.
So I looked high and low for some 100 shorts but never found any. So I gave up and swapped the 118 drilled nickel plated 60s back in. The 1500 to 2000 lean spot came but but with less vengeance than before. I think the 42 longs are doing something.
The mixture screw could also be backed out into its range again.It seems the solution is to get a set of small drill bits and choose a size between 90 and 118, then drill a spare set of nickel plated 60s. Shouldn't be too hard. Somewhere mathematically in the middle around 105 or so should do it. Thoughts?
Last edited by Jeff20B; 03-24-15 at 11:38 PM.