Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
erratic idle
Mr Hand:
I had primary throttle shaft bushings installed into my baseplate but still have an unsteady idle. Some propane down around the RH side of the carb down by the secondary throttle shaft hole smoothed it right out.
Obviously a vacuum leak thru the shaft hole but is it common to leak there? Can bushings be installed to fix this?
Mr Hand:
Hello? This thing on?
71vette:
I had a very similar situation with the idle after I installed new primary shaft bushings. I sprayed carb cleaner at the secondary throttle shafts and sure enough, the idle smoothed out. If you read through the history of posts, you will find that the rear throttle plates should seat themselves which requires some play in the secondary shafts. If you put your hand over the airhorn when it is running, does it idle better? If it does, you may have a vacuum leak (other than by the secondary shafts) or you may need more idle fuel.
Because I wasn't using the original carb and had taken a core and rebuilt it to Cliff's specs, I had to open up the idle down channel restriction as well as the idle mixture screw openings using one of Cliff's option settings. It idles the best it ever has. (454 with mild cam)
I didn't see any other details about your vehicle so if you can provide more information on make, engine and the work you've done on it, I'm sure there will be others on the forum that can provide some excellent suggestions.
Cliff Ruggles:
We can install 3/8" bushings for the secondary throttle shaft.
Before doing that, I would remove the throttle body and check to make sure the secondary throttle plates are fully seated when closed, shaft not bent, twisted, etc....Cliff
Mr Hand:
just rebuilt the carb using one of cliff's kit' and although the idle improved and seems a bit rich at idle (oww my eyes burn!) the engine falls flat on its face under anything past 1/4 throttle........driving away from a stop under anything more than softly on the gas pedal results in hesitation, stumble, bog and backfire......backfired so bad it blew out the muffler! !@#@%*@!
In park it tachs up with no problems this only happens under medium engine load.
Distributor rebuilt and recalibrated by suntuned aka Bob Davis so safe to assume it's not ignition. Timing set to 12 degrees BTDC and jumps up when the vacuum advance is hooked back up......using manifold vacuum.
Low compression Pontiac 400......stock cam
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