surging

[jazak5]

1969 barracuda fast back 340 /auto/rebuilt 4612sa avs carb

suddenly started to surge while cruising at 55mph//never had this problem//with a 1yr old rebuilt carb

mash the throttle//no response !! but will hold 55mph

fuel pump measures 4/5 psi how ever hard to measure flow

cut fuel filter open // some what clean//replaced still have issue

will take carb apart to recheck everything

have new //sending unit sock/retainer wrench/gasket //tank to filler neck seal//

any help??

can you drop the tank without taking the fill neck/rear seat/ seat pan// out ??

 

[Bewy]

I presume you are measuring the FP with a gauge? If so, & getting 4/5 psi that means the carb is getting sufficient fuel. So you can rule out fuel delivery to the carb.
What do you mean, 'no response'??? Car stops, backfires, somebody turned the key off?
Check that the AV did not come loose. If all checks out, disassemble carb & chreck thoroughly.

 

[BobW]

.I had a similar issue shortly after rebuilding the carb. Slow steady throttle was fine, Hit the throttle hard & it would surge or buck.
I had used the thicker 1/4" gasket and found the carb needed to be tightened to the manifold, took about 3/4 turn on the nuts.
It was loose enough thaty the additional demand from full throttle caused a vacuum leak between the carb & the manifold.
Simple enough to check!

 

[pishta]

Surging is lean....there is probably a vacuum leak somewhere. you want a vacuum gauge in the car if possible or just start hunting with a mighty-vac or pair of pliers pinching vacuum lines and listening for an RPM change.

 

[AJ/FormS]

suddenly started to surge while cruising at 55mph//never had this problem//with a 1yr old rebuilt carb

mash the throttle//no response !! but will hold 55mph

By any chance was this right after filling up?

Running lean can be getting extra air. But
can also mean not enough gas or
contamination of the gas..... like water, or
the wrong fuel for the tune; like E20 gasohol in a premium-tuned engine.
Or something really simple like the metering rods not working.