Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

erratic idle

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Cliff Ruggles:
What is the carburetor number?

Is the engine completely stock and the one for the application?.....Cliff

Mr Hand:
17058274

yes

Cliff Ruggles:
Rebuilding the carburetor with good parts and correct settings should have it working fine for what you are doing.  Were the idle tubes removed and cleaned during the rebuild?  Did you adjust the APT back to it's original setting.   Power piston hanger has the metering rods exactly even.

The backfiring situation to a point where it blew up a muffer is most likely ignition related.  The engine quits firing the plugs, fuel builds up in the exhaust system, then it starts firing again and ignites the fuel.

Do you have control of the idle fuel with the mixture screws?

Is the accellerator pump delivering a good shot of fuel when the throttle is moved quickly?

Was manifold vacuum used to the advance before the carb and distributor were rebuilt?.....Cliff

Mr Hand:
 Were the idle tubes removed and cleaned during the rebuild?

no but they were cleaned with solvent & brake clean and appeared to be clean when looking through them with magnifying glass.


The backfiring situation to a point where it blew up a muffer is most likely ignition related. 

agreed although this is the third Bob Davis HEI I've had him do and all prior units have been perfect. Not sayin this one is ok but.........


 Did you adjust the APT back to it's original setting.   Power piston hanger has the metering rods exactly even.

no wasn't sure how to


Do you have control of the idle fuel with the mixture screws?

yes


Is the accellerator pump delivering a good shot of fuel when the throttle is moved quickly?

yes


Was manifold vacuum used to the advance before the carb and distributor were rebuilt?.

yes but the car was never driven after the initial rebuild

Cliff Ruggles:
Idle tubes can not be cleaned with compressed air and any sort of carb cleaner of solvent.  They "varnish" inside, and the only way to effectively clean in and under them is to remove them. 

It is possible to "rod" them out with a piece of .030" spring or music wire, but we highly recomend removing them, to effectively clean in and under them.

We also recomend installing a removable set screw over the APT adjustment, to fine tune the part throttle A/F ratio without having to take the carburetor apart.

The items mentioned above will help make sure the rebuild is done correctly.

Some of the symptoms mentioned still don't sound carburetor related, at least the backfiring and blowing out the muffler thing.......Cliff

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