Cliff's Quadrajet Parts and Rebuild Kits

Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: EricPeters on July 17, 2015, 11:14:13 AM

Title: WOT falls flat/whether air door tension is loose or tight
Post by: EricPeters on July 17, 2015, 11:14:13 AM

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?

Title: Re: WOT falls flat/whether air door tension is loose or tight
Post by: EricPeters on July 17, 2015, 01:19:24 PM

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?
 

Title: Re: WOT falls flat/whether air door tension is loose or tight
Post by: Cliff Ruggles on July 19, 2015, 09:42:42 AM

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

Title: Re: WOT falls flat/whether air door tension is loose or tight
Post by: EricPeters on July 20, 2015, 10:26:44 AM

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.

Title: Re: WOT falls flat/whether air door tension is loose or tight
Post by: Cliff Ruggles on July 21, 2015, 04:28:32 AM

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

Title: Re: WOT falls flat/whether air door tension is loose or tight
Post by: EricPeters on July 21, 2015, 10:09:23 AM

Thanks, Cliff.

I plan to eliminate each possibility. Can you tell me how to go about ordering the appropriate needle/seat assembly? The carb is original to the car ('76 Trans-Am).

On the pump: I plan to disconnect the fuel line at the carb, hook the carb up to an "IV" fuel source and measure the pump output. How much fuel should flow into a bucket over what amount of time?

If the pump is inadequate, do sell (or can you recommend) a replacement?

I am pretty certain it can't be the lines (new and 5/8 diameter) or the tank (also new)...

   

Title: Re: WOT falls flat/whether air door tension is loose or tight
Post by: Cliff Ruggles on July 28, 2015, 07:31:58 AM

I'd try the larger .145" seat we sell.  If you still have problems, the fuel pump or fuel delivery system in inadequate for the power level.....Cliff

Title: Re: WOT falls flat/whether air door tension is loose or tight
Post by: 77cruiser on July 28, 2015, 08:43:07 AM

If you can pump a gal. in 30 sec. you should be good.

Title: Re: WOT falls flat/whether air door tension is loose or tight
Post by: Cliff Ruggles on July 30, 2015, 05:02:41 AM

Fuel delivery required depends on power level and how fast the vehicle is.  For 455's capable of running into the 11's, your fuel delivery system should be superb.  Mine will fill a gallon jug in just over 20 seconds, and I've never had the first issue to date running nearly into the 10's in the 1/4 mile.....Cliff