General Category > Quadrajet Carb Talk and Tips

AFR dropping just off idle

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77cruiser:
I tapped mine to 6-32 & did the setscrew deal.

Cadman-iac:
  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

Kenth:
I have found that 1977-79 Cadillac 425 units has about .078" lower air bleeds and about .049" idle needle holes.

If the throttle blades are in a good location at idle speed and no nozzle drip occurs there is no need to enlarge the idle bypass air supplement.

FWIW

Cadman-iac:
 No, there's no nozzle drip, I've checked it for that and to see when it begins to pull from the main system.  I don't remember exactly when it begins pulling from the main system, I want to say around 1200 to 1300 rpm, but I've slept since I checked and my memory resets every night after the reboot.
 As for throttle position, I haven't tried to see how much farther it will close, but if it's not there now it's almost there, so I don't think that's an issue.
  I did enlarge the mixture screw holes to .078 to try to eliminate the off-idle lean condition it had. That's not nearly as bad as it was now.
 The more I drive it and watch the AFR gage through the various rpms and loads, the more I think I understand what is going on. I just want to be sure I'm not misinterpreting what I'm seeing.
 I couldn't really tell how fast the engine was running because my old tachometer was bouncing and I couldn't get it to clear up, so Tuesday I got my new tachometer from Summit Racing (made in America)  and I can tell much better what's going on.

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