General Category > Quadrajet Carb Talk and Tips

AFR dropping just off idle

<< < (2/3) > >>

quadrajam:
You can go ahead with .086 on the idle mixture holes and if thats too much
you can screw the mixture screws back in some. same/same

QJ

Cadman-iac:
 Didn't get a chance to work on it yesterday,  I'll try enlarging the idle ports today and see what happens.

Cliff Ruggles:
If you are working with a later model carburetor with a big lower IAB you can shrink that bleed down slightly to put more fuel where you need it without increasing IFR's or DCR's.  I do this on some of the later model Buick, Caddy and Chevy units to correct that issue.....

Cadman-iac:
  Cliff,
 I just posted a few questions in another thread on this 17057230 carb about inconsistent AFR's between idle and high idle as it warms up. If I shrink the lower idle air bleed size, you're saying that would level out the AFR through the lower rpm range? Or did I misunderstand what you meant?
 They are at .078 right now, which is the factory size, so if I wanted to shrink them, how would I go about it?

novadude:

--- Quote from: Cadman-iac on February 19, 2025, 11:57:30 AM ---  Cliff,
 I just posted a few questions in another thread on this 17057230 carb about inconsistent AFR's between idle and high idle as it warms up. If I shrink the lower idle air bleed size, you're saying that would level out the AFR through the lower rpm range? Or did I misunderstand what you meant?
 They are at .078 right now, which is the factory size, so if I wanted to shrink them, how would I go about it?

--- End quote ---

I think that is what Cliff is saying.  From my q-jet experiments in carburetion, I've found that they seem to run better with lower IAB in the 0.062 -.067" range.  For me, it seems to help smooth the off idle.

In theory it should also deliver less fuel at heavier part throttle, since this air bleed tends to become a fuel feed when the throttle blade edge gets close to the bleed. 

I've used a punch and an old accelerator check ball to shrink the bleed, and I typically qualify the hole with a #52 (0.0635) drill after swaging it smaller with the punch/check ball.  Curious to hear if others have had similar experience? 

Navigation

[0] Message Index

[#] Next page

[*] Previous page