The Stovebolt Site Forums The Shop Area Engine Shop Carburator Problem

I have a 1941 Chevrolet 1.5 ton military truck that has about a 1955 235 engine in it. The Carburator is a Rochester Model B. The truck sat idle for some time and the carburator was doing bad things when I started it. So, I removed it and cleaned it up, put in a new needle valve and gaskets, carefully set the float level and drop and re-installed it. I am using fresh gasoline from a can on the fender and an electric fuel pump. The truck starts OK and seems to idle reasonably well - the idle does respond to adjustments to changes to the mixture screw. The problem is that when the engine is running faster, maybe 2000 or better RPM, with steady throttle, it seems to cut out or hesitate. But, if I pull out the choke just a little bit it clears up and runs fine. Anyone have any experience with this simple old carburator and why it might require some choke to get enough fuel? Sid

Did you make sure that you cleaned up the power piston so it would move up and down in the bore? Have you checked the point gap/dwell/timing? Have you checked that the vacuum and mechanical advance are working correctly? All of those tend to sieze up and break when the engine sits up for a while.

Also, make sure all the vacuum passages in the carb are clear, and that you are using the spacer between the carb and manifold that has the groove cut in it to allow vacuum to reach the innards of the carb. It has a hole in the flange.

Also, make sure you have an air cleaner installed before you worry about it. They take enough pressure drop to mimic a part choke.

what kind of choke is it? if it is a heat coil type you may need to adjust the coil. if it is an electric, throw it away. if it is manual, just play with it. my 235 isn't rebuilt and it skips or hesitates at about 70 mph just a little. it used to do it real bad until i got the dwell set correctly. also the electric fuel pump may be part of the problem. i tried one with very little success, my 235 liked the manual pump much more.

Thanks guys for the suggestions. I did remove, clean up, install new points in the distributor. Carb. is, I think, clean and the vacuum operated rod is free etc. But, for some reason, it just isn't seeming to suck in enough fuel without a little choke. Any chance the main metering jet is too small? Might be for some other engine. But as you say, best to just live with it I guess.
Sid

Before just living with it I would really suggest trying the manual fuel pump. It really made a difference with mine and it only cost like 15$. It is well worth the money to see if it will run better.

I ended up replacing the fuel pump on my '46 (after it completely crapped out). Thinking back, there were warnings.

If everything else is where it should be, but you are getting variation in engine RPM's above idle at any particular throttle setting, then it sounds like variable fuel delivery or vacuum leakage, or a combination thereof.

Fuel pump can be a easy culprit. If you are gravity feeding the carburetor during testing, you may not have enough fuel delivery to the carb at continuous engine RPM's greater than idle.

If the fuel pump is old, sat for years, and worked when you parked it, that could be the culprit.

Golly, it's fun to trouble-shoot from miles away, and it don't cost much either.

Drive that ol' '41 up to Jarrell someday.