General Category > Quadrajet Carb Talk and Tips

Dance steps, need some help!

(1/1)

Cadman-iac:
  I'm trying to understand what the relationship is between the APT, the idle circuit and the main circuit.
 The APT seems to have an effect on both the idle and the main throughout the rpm range. 
  My idle mixture is slightly rich, it runs around 12.2 to 13.0, but I have a persistent lean condition just above idle that I can adjust out somewhat using the APT, raising it reduces the lean off-idle condition, but it also enriches the idle, and main circuit at all RPM's, in my opinion by too much.
 Currently I have the main AFR running around 14.5-15.5 at a cruise rpm of 2500-3000, but between 600 to about 1200 rpm at light throttle the AFR goes extremely lean, as much as 17.5 and higher, and I'm at a loss as to how to correct this.
 How do you richen up the off-idle mixture slightly and not change the higher rpm mixture?
 I've opened up the bypass air to  .095" from .039",and the IDCR's from .046" to .057", and the UIAB's from  .048" to .061" in an effort to get the idle circuit to work better in the higher RPM's.

 It's a delicate dance apparently, and i flunked out of dance class. Where do I go from here?

 Do I raise the APT, drop one jet size, and lean out the idle mixture slightly to compensate for the higher APT?

 This is a Cadillac Quadrajet on a SBC, #17057230, and it's got a main nozzle air bleed size of  .055, whereas the typical Chevrolet nozzle air bleed is only  .029. Would this be the problem, and if so,  how do you fix it?

Cadman-iac:
 How big can you go with the IDCR's? I'm thinking about increasing these to see if it would eliminate this lean off-idle condition.
 Even the high idle AFR is lean when the engine is cold. I was just looking at the base plate, the idle transfer slots are not exposed at the base idle, and the AFR is good at that point if I adjust it, but doing this really makes the off-idle AFR go too lean.
 I've been going with a richer idle to get a less lean off-idle mixture. Now im thinking that is the wrong approach.
  Is a bigger IDCR the better way to correct this, but how much bigger?
 I believe if I use bigger IDCR's, I can reduce the idle mixture screws to compensate for the increase in available fuel, and the increase in available fuel should correct this lean condition.
  Or do I raise the APT and drop a jet size  and increase the idle mixture screws?
 Just thinking out loud here, so to speak.

 My sincerest appreciation for any help here, thank you. 
  Rick

Navigation

[0] Message Index