Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

WOT falls flat/whether air door tension is loose or tight

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EricPeters:
I've got an exasperating problem. '76 Trans-Am, 455/2004R automatic, 3.90 gears. I have Cliff's recommended jets/metering rods installed. Car starts immediately, runs perfectly except when you floor it. Then what happens is the engine revs to about 4,500 and then - falls flat on its face, like you turned the ignition off. If I back off the gas, it recovers. I have been carefully making adjustments to the secondary air valve, 1/4 turn of the screw at a time - and it seems to make no difference whether the tension is almost nill (the doors flop open at the lightest touch) or half-to-three-quarters or more a turn of the adjustment screw tighter.

I am stumped. Any thoughts?

EricPeters:
Wanted to add: I am suspecting a fuel delivery issue (fuel bowl running dry under WOT) but wondering how this could be given:

New high volume fuel pump, new (larger diameter than stock) fuel lines.

Float level is set 1/4 inch, per Cliff.

The engine is a mild street engine with a repro Ram Air III cam. Nothing crazy. Edelbrock Performer intake.

Everything except WOT and the the thing runs great and even WOT... for a few seconds... until it falls flat on its face.

Cliff mentioned replacing the spring and cam for the secondary air door... thoughts?
 

Cliff Ruggles:
What size N/S assembly did you install.  Symptoms for sure are fuel delivery related....Cliff

EricPeters:
Hi Cliff,

IIRC, it was the one in the kit. But maybe I need a higher flow unit? If you think so, let me know and I will place an order right away.

Cliff Ruggles:
If you have plenty of fuel pump, and no restriction before the pump, then the problem will be with the N/S assembly being too small......Cliff

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