Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Dieseling
Chevynation:
The bypass holes are already pretty big it appears. If my idle screw was backed out that far and it was still idling at 750 then I would say I have too much bypass air and it’s running on from that and not the transfer slot which I thought before I removed the carb. Doesn’t anyone know the amount of transfer slot exposure for a quadrajet? Throttle blades are 90 degrees at WOT and fully close no light can be seen. The stop that’s on the primary shaft that the idle screw makes contact with looks like it should make contact with the main body for a stop but I’m coming up a little short. Not sure if this is a big deal or not but just something I noticed.
Kenth:
I think you are measuring the idle tubes in the upper end? The restriction is in the lower end.
As for the off-idle slots they are exposed some in some units adding some idle mixture, use the idle needles to adjust the amount of idle mixture.
And the idle bypass air restriction is measured from underneath on the plate.
77cruiser:
I've always seen more transfer slot on a Qjet vs. Holley, & it seems the later ones have more yet.
What you're showing for transfer slot is pretty good IMO.
Chevynation:
It looks like the base plate idle air holes moved in 73 and my main body is a 75. So really my idle air holes between the body and base plate are misaligned. I looked at the carb and it looks like the gasket has enough of an opening to allow air to still allow it to work. Just thought I’d share that. I’m measuring the idle bypass holes on the bottom now. I looked at another quadrajet and there will be transfer slot exposure with the blades closed so that’s fine.
Chevynation:
0.136 Idle bypass air. I’m not positive but the hose on my choke pull off valve was loose and I put my vacuum gauge in it while on the choke pull off and it wasn’t holding. Tried a different hose and it worked fine. I’ll put it back together as is to see if that was a vacuum leak.
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