Accelerator pump problem?

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May 1, 2009
Since I got my '74 back on the road I have discovered a very bad stumble during initial throttle application (usually accompanied by what sounds like some backfiring out the carb). I believe I have timing set correctly (at BB).

Suspecting the accelerator pump was the problem I found that when throttle is quickly opened (without the truck running) only a trickle of fuel comes out of the accelerator pump outlet. The plunger moves pretty slowly as well. Shouldn't it be a reasonable stream even with it not running?

I plan to try it running tonight but just wanted to check before I stare into the mouth of a backfiring carb.

Answering my own question: at least assuming there is adequate fuel remaining in the bowl.
i just solved my accelerator pump dilemma this weekend.. similar symptoms as you are having.. couldn't get a good squirt from the accelerator pump.. and stumbling during primary acceleration.. i was needing to use starting fluid to start it for the previous 2 weeks.

the problem turned out to be the ball bearing that sits under the accelerator pump.. it was a bit rusted/worn and was stuck down in the hole not allowing the gas to squirt properly.

replaced that bearing and it starts and runs great.. no more throttle hesitation either.
Thanks voyager.

It looks like I will need to remove the air-horn to service the pump - correct? The carb was recently rebuilt by Jim C. So I suspect a piece of debris is causing the problem.

I've had troubles on fresh rebuilds where the plunger didn't want to seal properly too. May try soaking the leather cup in some light oil and flare it out a bit when you put it in. If you just had it rebuild, it may have shrunk a bit sitting without any fuel, and sometimes they just won't re-expand after getting put back in service.

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