Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

opinion on primary rod / jet change

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Cliff Ruggles:
Couple more things to add here.  We do NOT tune WOT fuel with primary jets.  77 jets are PLENTY for what you are doing as are AX or DA secondary metering rods.  Look elsewhere for your issue going to and at WOT.  Fuel inlet seat diameter, fuel delivery to the carburetor, ignition issues, etc.

I'd also take a look at the choke pull-off release time if you are experiencing this problem the moment you get into the secondaries.  Also look at the hanger to make sure the arms aren't bent up or down or both. 

This changing the main jets is NOT going to be the cure here.  Main jet size is adequate if you have good power and performance at heavy part throttle W/O the secondaries.  The later Chevy carbs with the huge MAB's do well with jets in the .075-.077" range for most applications.  I find however that employing the APT system in the baseplate and/or going to smaller primary rods really helps them out.

I'd also add here that we DO NOT tune a carb richer for a larger or more powerful engine.  Matter of fact all of these engines operate pretty much in the same range far as A/F goes.  You may have to add some idle fuel and idle bypass air for big camshafts, but richening up the carb clear across the load speed range isn't typically needed.  Matter of fact the better job you do on choosing the parameters for your new engine the LESS fuel it's going to need far as A/F goes and more efficient it will be.  These choices include the compression ratio, squish distance, squish area, cam events, head flow and combustion chamber shapes........

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