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Old 01-16-2011, 07:17 PM
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Air Bleed Help - Holley

383 with Proform 750 Carb, Vac Secondaries
10.7:1 Cam: VooDoo 60133 249/255 @ 0.050 .585/.600" lift +1.55 Rockers.
PP Crosswind Intake

Idles a tad rich at 13.1-13.8 AFR
Cruise is a tad lean at 15.5-16.5 AFR (Switching to 39 IFRs next)
.037 IFR, 78 Primary jets/86 Secondary jets, 4.5 Primary PV no Secondary PV
30cc pump w/ Green cam 1st hole. (Largest shot but shorter duration than pink) 35 squirter
Throttle plates right at .020" of transfer circuit on primary and secondary blades. Idles at 1100rpms. 4 corner screws turned out 2.25 turns.
Timing: 21* intitial, 36* total by 3200rpms. Vac can adjusted all the way out for 12* more max.

I've done the bread tie on the secondaries and they seem to start coming in around 2500rpms. Needle valve on adjustable secondaries is out 2 full turns.

Here's my issue. With WOT when I first floor it, say 2500rpms in 3rd gear, I get an AFR of about 13.5. It jumps to 12.5 by 3500 rpms at which point it keeps rising to 12, then low 11's by 6000rpms, touches high 10's by 7000rpms when I shift.



What would cause the AFR to keep getting richer as rpms go up. Do I need bigger high speed air bleeds? Looking to keep things around 12.5 at WOT, right? Could rear jets be too large? The vac secondary would add that rich condition over time, right? I went up 8 jet sizes from the fronts due to lack of the power valve.

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Last edited by Landshark928; 01-16-2011 at 07:24 PM.
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Old 01-16-2011, 07:26 PM
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The primary jetting is too rich.
Go to a #73 pri jet and make the pri idle air bleeds smaller.
What size are all the air bleeds?
Most of the time you are "cruising" you are actually on the idle /off idle circuit.

You are compensating with extra rich pri jetting for a lean off idle/transition condition. (pri idle air bleeds). Then when you are up on the main jets, its way to fat.
is this a auto trans car or manual trans?

Last edited by F-BIRD'88; 01-16-2011 at 07:33 PM.
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Old 01-16-2011, 08:17 PM
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Quote:
Originally Posted by F-BIRD'88
The primary jetting is too rich.
Go to a #73 pri jet and make the pri idle air bleeds smaller.
What size are all the air bleeds?
Most of the time you are "cruising" you are actually on the idle /off idle circuit.

You are compensating with extra rich pri jetting for a lean off idle/transition condition. (pri idle air bleeds). Then when you are up on the main jets, its way to fat.
is this a auto trans car or manual trans?

5 speed manual.

I got the cruising part, I was already going up on the IFRs to compensate. High speed air bleeds are .036" front and back. Idle bleeds are 0.073" front and 0.67" back.

So, too rich on the main jets will continue to lower AFR as RPMs go up? I had the wrong info for my secondary jets, they are bigger at 88 not 86. Read the wrong line on the Max Jet conversion chart.

I'll try going back to the stock 72 front and 82 rear and see what I get. Along with the larger 0.039" IFR. I have 76/86 jets as well. Guess I may need some 74/84 as well.

I just got my wideband hooked up today. Prior I had gone with settings from a similar build 383 at about 540HP with the same carb, smaller cam but better heads. They had 82/82 with dual PVs. They had a similar issue going rich up top and added larger air bleeds to fix. I think mine gets rich earlier than theirs did. I am just over 500HP so figured I would be a step or two lower on the jets. I have vac secondaries and they don't. Guess I screwed the pooch guessing at that one. Now that I have the wideband, I can start low and work up again.

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Old 01-16-2011, 08:59 PM
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Ya you are beyond the normal jetting range for that carb.

You also have the idle air bleeds reversed.
Go back to default jetting, IFR's and reverse the idle air bleeds around front to back.

74-84 jetting 67 pri idle bleed 73 sec idle bleed.
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Old 01-16-2011, 10:29 PM
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Thanks Fbird!

I just figured (wrong) that if it was over jetted the AFR would be rich but flat. Not rising with RPM. I'll see what the 72/82 do while I order a set of 74/84 Max Jets.

So you think switching the idle air bleeds around from the stock 73/67 set up to a 67/73 will richen up the primary idle helping with tip in and cruise? Or should I go to 70's all around since the front and back throttle blades are exposing the same amount of both idle circuits? I noticed the Quick Fuel version of my carb has 70's all around and the Proform is 73/67. Jetting and IFRs are the same.
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Old 01-17-2011, 04:28 AM
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Hi Landshark928, Jetting and tuning these carbs is some fun but one needs to understand exactly what each jert is doing. i recently installed 2 Q650 Quickfuel drag carbs on my sb. The quickfuel are very similar in principle except they include emulsion jets. This adds even more tunability but with more frustration aswell!! I have tried to understand the basics first. Interesting is that the IFR feed both curb idle jet and transfer slot. If you want to lean the idle circuit then reduce the size of the IFR or increase idle air bleed but watch signal strength.Also interesting is that the main jets feed everything with the exception of the accelerator pump1 So the main jets just move the entire curve up or down. On the Quickfuel and proform I imagine all these jets can be changed they have been tapped . Also the air bleeds allow one to further taylor the curve. Bigger air bleed means less fuel more air but also less response ie slow or low signal strength. Ofcourse this is all very interesting but it is easy to loose track of things and forget that it is the fuel curve or AFR in all circuits that we are trying to establish. I have a situation where just off cruize I have a lean 15-16 AFR but for an instant then as mains come in AFR reverts to about 12.5. I then have the added case of water meths coming in which fattens it up to around 10. Still have to do alot more tuning to sort this one out. Its all good fun and interesting . Keep a log book and map changes at every step. Obvioulsy a wide band AFR like you have is essential.
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Old 01-17-2011, 09:38 AM
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When I did mine I made my own custom pri idle air bleed by soldering it up and drilling it to .062" (1/16) and then fine tuned it (trial and drive testing) a little at a time using the drill bit as a hone until it was just right. Doesn't take much. Ended up around .064" on mine.
The AFR gauge helps a lot.
You must get the idle and off idle circuit right before moving on to the main jetting.
It will be very close with the baseline main jetting.
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