Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

OFF idle issue

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Cliff Ruggles:
Without the APT functional you may have to install small rods instead. The "B" series rods were used in those carbs with the early APT system, and they really start to richen things up nicely as you raise them up and out of the jets and position the tapered section between the upper/lower sections further up in the jets.

I did that same carb number recently for a 455 Buick Stage one with a T/A cam in it.  We had the vehicle here, and I found that jet/rod combination perfect, but we did have the APT working and fine tuned it on the engine. 

In lieu of not having the APT screw out of the baseplate, another option is to bend the wire that the power piston post sits on up slightly.  It may take several attempts to find the ideal height, but still beats taking the top off the carb and changing parts......Cliff

Jeffs68:

--- Quote from: Cliff Ruggles on July 31, 2016, 11:58:20 AM ---Without the APT functional you may have to install small rods instead. The "B" series rods were used in those carbs with the early APT system, and they really start to richen things up nicely as you raise them up and out of the jets and position the tapered section between the upper/lower sections further up in the jets.

I did that same carb number recently for a 455 Buick Stage one with a T/A cam in it.  We had the vehicle here, and I found that jet/rod combination perfect, but we did have the APT working and fine tuned it on the engine. 

In lieu of not having the APT screw out of the baseplate, another option is to bend the wire that the power piston post sits on up slightly.  It may take several attempts to find the ideal height, but still beats taking the top off the carb and changing parts......Cliff

--- End quote ---

What rods do you recommend?

Cliff Ruggles:
I'd try a set of 39B rods

Jeffs68:
So, I've got the rods coming, as soon as I cant get to it, I'll post an update.

Thanks!

Jeffs68:
-UPDATE-

So, got the 39B primary rods installed today, fired her up and made some initial adjustments.

We're getting there, almost no OFF idle stumble, I think I may try to bend up the APT wire slightly per your original recommendation Cliff.

I need to get some other things sorted out, throttle cable, return spring and divorced choke. But we are making progress.

Was going to try going from manifold vacuum on the advance to ported at the carb, what do you think? Easy enough to try out.

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