Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Rebuilt qjet won't idle lower than 700 in gear

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Kyle:
Ok, I will reply to myself.

After reading up a bit more on the web and Cliff's book, I realize that the vac advance should be ported with no vac reading at idle. I also pulled my carb this morning and realized that the 4 bolts holding it down were barely tight. SO I'll fix all that today and see where we're at.

Kyle:
SO....

I tightened the carb down, unplugged the advance that was not ported. Got 18 in vac instead of 15 before. idle was easy to control and the carb behaved normally. Checked initial timing it is set at 12 degrees, not sure if I should lower that. Reconnected the vac advance to the ported source that is at zero when idling.

omaha:
ok sounds good . I am not sure what the spec was for idle rpm on that engine but im guessin 600 in gear (automatic trans). sounds about right to me. 

Kyle:
Yes the spec is 600 in gear, and 9 degrees mechanical at idle. The engine was rebuilt with a XE 256 cam and is 30 over. I guess I need to figure out wHat it is all in.

StillLearning:
It sounds as though you are making progress. Remember that timing will affect carburetion more than the other way around.  The ported vacuum slot is in Q-jets for primarily emissions reasons, a late fire cleans up the unburned fuel mixture. If emissions are not a big concern, tune to a normal vacuum source. IMHO
Regarding timing, tune to the best total timing. Aim for around 34 degrees total at around 2800-3000 rpm with just the mechanical advance (vacuum advance off and port plugged).  At 34 or so degrees total let it drop to an idle and see where your low idle timing is. If its close to spec and not rattling at the high rpm setting with the vacuum advance hooked up you are close to ideal timing.  If it "rattles"at high rpm, back off the timing a degree or two at a time until it doesn't rattle any more. You may have to adjust or replace the vacuum advance unit to better control when and how much it advances timing.  Once your timing is set right you will be in a much better position to tweak the Q-jet. It IS worth the extra time and hassle.  ;)

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