Accelerator pump problem?

[Adax]

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.

 

[zags]

Yes it should be a brief stream whether it is running or not.

 

[Adax]

Thanks

Answering my own question: at least assuming there is adequate fuel remaining in the bowl.

 

[voyager:01]

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.

 

[Adax]

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.

AC

 

[MoCoNative]

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.