Quadrajet Carb Problem

Q: Quadrajet Carb Problem

I have a 1968 Firebird 400 with a Quadrajet carb. The engine is idling to high (1000 RPM or so in drive) when warm with the choke open. The idle adjust screw is backed all the way out and the mixture screws are adjusted. No detectable vacuum leaks and the throttle linkage is loose at idle. The only modification is an open element air cleaner.

Any ideas as to why the car is idling high? If you think I need a rebuild, any suggestions for my daily driver?

A: Check the SECONDARIES …. these are always overlooked … and should be closed under an idle condition. If this isnt it then check the set screw that adjusts the butterflies.

A: I’d bet the problem lies in the orientation of your throttle linkage, throttle cable, or throttle cable bracket. Pull the keeper pin that holds the cable to the throttle linkage. Let the linkage relax to the closed position. Pull the cable all the way out with your fingers and hold it next to the point where it hooks to the linkage. My guess is that you will need to shift things around a bit to get the eye hole in the end of the cable to reach the throttle linkage connection point in its closed position.

A: I just hadthe same problem with mine .. I ended up looking at the petal itself , over the years it has been hit so many times that it was bent …{ my lead foot }… so it stayed about 1200 rpm … I had to rebend the petal to set it right

A: Did the problem happen all at once?If so is the choke step coming off all the way?This type of setup likes to bind.A little wd 40 or liquid wrench will solve the problem.My Bird stays parked alot so the linkage will bind and a quick shot with the spray and away I go

A: I’ve had that happen and the secondaries staying open were the problem as pointed out earlier. Another guess….Could it also be that the float needle is not seating, or might be worn out???

Is it possible that you did something out of the ordinary that might have caused the problem? Perhaps dropped a tool on the carb while working on your car and bent some carb linkage?

Another thought…. Is there a slow idle solenoid on the carb? Is it stuck?

My last shot at it…. You may have gotten to close to a Rice Burner and sucked it into the carb. No big deal. Just push it all the way in.. Your bird loves seed!

A: It’s either a vacuum leak or ignition timing. check your timing and make sure it’s at it’s proper setting. To check for vacuum leaks, unplug one vacuum line (from the carb) at a time and plug the port. If the idle is unchanged reattach the line and move to the next line. After you’ve verified that the lines and their accessories are working properly, take some WD-40 and spray it on the throttle shaft on the bottom plate of the carb. Next move to the carb gasket and spray all around it. Lastly, spray the intake manifold around the intake ports at the heads.

A: i would bet the front butterflies are not closing properly if so you might have some build up in the bores of your carb. look into the bores with a flashlight and see if you see any build up that sort of looks like water scale where the butterflies touch the bores when closed i hade this problem before you might can clean it but would be better with a rebuild

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