The Stovebolt Site Forums The Shop Area Engine Shop Acceleration but no idle. Carb prob?

This topic must appear somewhere on here but I can't seem to find search results.

1951 Chevy 3600 216
Rochester B Carb

New fuel pump installed last week and everything was great until yesterday. Truck sputtered and stalled but quickly recovered by pumping the accelerator and I made it to work. End of the day It restarted and I made it home with no issue. Today same story... started right up, went to work okay but coming home it sputtered a bit then stalled, and now will not maintain an idle.

It restarts fine. Pumping the accelerator pedal keeps it going but it stalls and stops when letting of the gas to idle.

If anyone can suggest a diagnosis page I'd be glad for some direction. If you have a good inkling about the problem I'd like to hear your theory as well.
Thanks,
Rog

(1) Defective electronic conversion in the distributor
(2) Burr on points changing both dwell and timing
(3) Partial clog of idle circuit in carburetor.

Jon

Gonna choose (3).

When changing the fuel pump, you might have had some trash enter the line and make it's way to carb and settle in the idle circuit.

I'll side with Roy...particularly if there's no filter between the pump and Mr. Rochester. It is possible even though the pump is new that some junk was inadvertently left inside when it was assembled. Have you had previous trouble with the carburetor and idling?

Here's a sneaky trick that has worked pretty often for me. Open up the idle mixture screw a couple of turns, then rev the engine up close to cruise RPM and either close the choke or clap your hand over the top of the carb. Do this several times. If there's a tiny bit of debris stuck in the idle circuit, the quick shot of high vacuum will draw liquid gasoline through all the passages in the carburetor and maybe flush it out. If it works, fine- - - -readjust the idle mixture and press on. If not, you're going to have to open up the carb and put high volumes of air through every passage to clear the clog.

I hope you didn't use thread tape on any of the fittings of the new pump- - - - -tiny slivers of that stuff love to clog carburetor passages!
Jerry

Jerry, do you recommend using any type of sealant on the fittings between the fuel pump and carb inlet?

Not Jerry, but NO! on the sealants. New fittings will seal. If you absolutely certainly cannot sleep at night if you didn't put something on the threads of the fittings, then 1/2 drop of blue loctite.

Jon.

Brass fittings with pipe threads in aluminum castings shouldn't require any type of sealer. Just don't overtighten them and crack the casting. A long time ago, I used to use a product called "Leak-Lock" which was designed for high pressure refrigeration fittings. It was a thick liquid that resembled blue Loctite. Using sealer on fittings that operate at the pressure of carbureted fuel systems is pretty much redundant.
Jerry

Thanks all;
No troubles previous and I first also thought debris upon replacing the fuel pump.
And no to tape thread.
I'll try my luck at the suggestion from HotRod
Thanks again!

Re: the thread sealer question...please remember your fuel pump should not produce more than 4 psi...5 at the very most and 2.5 is in my experience just perfect for a 235 or 216 with a 1bbl carburetor. You aren't dealing with the same 50 to 80 psi your city water supply provides.