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81
Quadrajet Carb Talk and Tips / Re: 17077230 jet/rod sizes from the factory
« Last post by Cadman-iac on February 19, 2025, 05:13:02 PM »
  It does make your eyes water if you stand near the tailpipes when it idles, but it runs and idles great.  I don't want it to wash the cylinder walls from too much gas, but I don't know at what point it would be too much.
 My wife is complaining that she can smell gas, as if it were leaking, but I believe it's the exhaust she smells. I will check the fuel return line for leaks just in case. That's the only line that has any kind of pressure in it now.
 The vacuum at 500 rpm in gear is 15 inches, and in park it idles at 600 with a vacuum of 16 inches.
 I can set the AFR to 14.7 at idle but it doesn't run as smoothly as it does at an AFR of 12.5-13.0, and the vacuum isn't as high either.
 
 Another question, at a part throttle cruise at around 3000 rpms, the AFR can go up to 16.0-16.5, which I think is normal for a light load at that rpm, isn't it?  Or do I need to worry about that and adjust accordingly?

 Thanks for any and all advice.

 Rick
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Quadrajet Carb Talk and Tips / Re: 17077230 jet/rod sizes from the factory
« Last post by quadrajam on February 19, 2025, 04:41:12 PM »
Set the idle as normal, use a vacuum gauge if it helps. If it runs good and dont skip or stink
leave it be. AFR meter best used for cruise and WOT on a warmed up engine. As far as engine damage....not gonna happen at idle or light loads.

QJ

83
Quadrajet Carb Talk and Tips / Re: AFR dropping just off idle
« Last post by Cadman-iac on February 19, 2025, 04:32:19 PM »
  I just realized I gave the wrong size on my lower idle air bleed. It's actually at .048, not  .078. The. 078 is the mix screw hole size.
 So what would I do now, increase the bypass air holes, they're at  .039 which is the original size for a 425 Cadillac.  If so, how big should I go?

 Rick
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Quadrajet Carb Talk and Tips / Re: AFR dropping just off idle
« Last post by 77cruiser on February 19, 2025, 03:41:14 PM »
I tapped mine to 6-32 & did the setscrew deal.
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Quadrajet Carb Talk and Tips / Re: 17077230 jet/rod sizes from the factory
« Last post by 77cruiser on February 19, 2025, 03:38:47 PM »
Bigger idle air bypass would make it leaner. Your idle looks good, highest rpm/vacuum?
How does it run?
86
Quadrajet Carb Talk and Tips / Re: AFR dropping just off idle
« Last post by novadude on February 19, 2025, 02:06:31 PM »
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?

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? 
87
Quadrajet Carb Talk and Tips / Re: 17057512 factory specs
« Last post by novadude on February 19, 2025, 01:50:38 PM »
Kenth... your post about main nozzle air bleeds intrigued me.

Let's say you have a Chevy carb with the 0.029" bleed vs a Cadillac carb with an 0.050" air nozzle bleed.  Assume all else is equal (the other two MABs, idle circuit, jets primary rods, etc).  How would this affect the fuel curve?  I would assume that the larger main nozzle bleed would delay start-up of the main system, and maybe require a larger main jet to maintain the same fuel curve?  Just curious if you have any experience with how different main nozzle bleed sizes typically impact the calibration requirements in the rest of the carb?  This is one area of a q-jet that I've not seen discussed often.
88
Quadrajet Carb Talk and Tips / Re: AFR dropping just off idle
« Last post by 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?
89
Quadrajet Carb Talk and Tips / Re: 17077230 jet/rod sizes from the factory
« Last post by Cadman-iac on February 19, 2025, 11:48:26 AM »
  Ok, I've got this carburetor on a 350 Chevrolet and when I first start it the AFR is between 14.5 - 15.0, then as it warms up and the choke opens up, the AFR goes up to 15.4 - 16.0 on the lowest of the high idle steps. Kick it down and the AFR drops to 12.8-13.0, which I guess is ok.
 My question is, would bigger idle by-pass holes help this to level out?
 Or is this normal?  I've never constantly monitored the AFR before, and this carb having not been set up for this engine originally,  I'm not sure what to expect.
 It runs really good, but I'm just concerned that I might not have it set just right and I don't want to damage the engine.
 The carb has the following specs right now:
Idle tubes- .040
Down channel restriction-.050
UIAB- .048 , original size
LIAB- .048 , original size
By-pass air- .039 , original size
Mix holes- .078
Float- 13/32"
PAB-Body- .039 , original size
PAB-Air horn- .070, original size
Jets- 72
Pri. Rods- 44 , Cliff's rods
Sec. Rods- DS , original
Hanger- T , original
Sec. Air tubes- .028 , original size
Sec. Well holes- .039 , original size
Air spring- 3/4 turn
PP spring- Cliff's red one, 4-12" vac?
APT set @ 2 1/4 turns
Acc. Pump lever hole- inner


  I'm also concerned about the 12.8-13.0 AFR at idle, is that too rich? If I lean it out at idle, the high idle goes leaner as well.
 Thanks for any advice regarding this. Rick
 
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Quadrajet Carb Talk and Tips / Re: My favorite Quadrajet rebuilding tools:
« Last post by Pav8427 on February 16, 2025, 09:22:54 AM »
Yes just pulling the two surgaces parallel with help of heat.
The 250* is only initial heating of jig/carb then letting cool over night in the oven.
Actually the most time involved in the whole process.
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