Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Poor Idle On Rebuilt Carb

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D Denzin:
I can't get my Rebuilt Carb to Idle decently.
It surges.   When it Idles at lower speeds it seems labored. It is inconsistent idling. Speeds up, drops down runs rough, if I blip throttle it'll idle faster, eventually will idle down and resume rough idling and surging. I have to adjust Idle screw out like 3 turns to get it to stay running. Then it runs at about 2000rpms before it seems to smooth out.

Specs.
Pontiac 65 326 HO with 9.2:1 comp.
Cam is basically very close to stock.
carb 17057253
Engine is rebuilt a couple of years ago. Switched carb from original AFB and Intake to Q-Jet and Edelbrock alum intake.
Car ran good with old set-up.

Was rebuilt using kit from Cliff and his recommendations about a year ago. I haven't had the time to mess with it until lately.

Jets .073
Metering Rod .044
Idle Tube .034
Idle Down channel .043
Upper Idle Air Bleed .070
Lower Idle Air Bleed .070
No holes in throttle plates
Idle bypass Air .081
Holes under Idle Mixture screws .090
Air horn Air Bleed .070
Main Body Air Bleed .029

I have checked for Vac leaks with a unlit propane torch. I have disconnected Dist Vac advance. I have disconnected Vac Gage supply. All with no effect. I even supplied propane into the disconnected open vac supply for the gage and it made no diff. Right now I have mixture screws out 2 1/2 turns. Adjusting them in and out has minimal effect. They will cause the engine to get rougher if I screw them way in. I have adjusted the APT in and out thru its full range and it seems to help being set almost all the way out.

Any Ideas on Where to go?

carmantx:
sounds like you have too much idle air possibly.  With the idle bypass and .034 in the tube.

D Denzin:
Trying to understand, too much idle air.
I can't get it to idle at all unless I open the throttle blades by turning the idle adjustment screw on the throttle linkage about 3 turns. My eyes are burning at times from the exhaust, thought that was a symptom of too rich.
the best I can get is by turning apt all the way up.
Any easy way to test if I have too much idle air?

D Denzin:
Big improvement. I disconnected the PCV hose from the carb and capped it. WOW. Now i can get it to idle down to 750-800.
I reconnected the dist advance to the manifold vac. source on carb.
I can adjust the idle speed down using the screw on the throttle linkage to the point that its not even touching.
At that point I tried to turn in the mixture screws to get the idle down. Still can not get the idle down before the engine starts to surge, run rough and die.

When adjusting idle mixture screws and even idle speed it seems odd in that I can make an adjustment, I can see a response in a second or two, then in about 5 to 10 seconds the idle will continue to deteriorate surge and get rougher and rougher. I can blip the throttle 2-3 times and drop it back to idle and it'll be fine for about 10 seconds or so. Then it continues to get worse till it will eventually die.

So now I'm at the point that it will idle decently, a littler faster than I'd like, for about 10 seconds, if I let it sit it eventually will die. I can speed up the idle to about 1000 and it will stay running but then its idling too fast.

Any thoughts?

429bbf:
id say your float is ether set to high or your needle and seat are leaking ,or your seal on your seat is leaking . what your saying is you are flooding at idle? did you get the gasket under the seat nice and clean before you installed the new one?and did you install a new gasket under the seat. i hate to ask these questions but one little spec of crap will cause the problems you have. do you have a choke is the pull off working?is the choke wide open?fwiw

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