The Stovebolt Site Forums The Shop Area Engine Shop 235 chevy rough running engine

Just bought a 54 Chevy 3100 half ton truck. I haven't worked on one of these for forty years but I think it should run smoother than it does. It feels as though it has a fouled plug or wire but that is all new. The plugs are burning rich.
The following was done while in neutural and parked. It runs rough at any RPM and because of a possible bad accelerator pump it has a dead spot when accelerated.
It has the Hydra-matic transmission.
It has a B Rochester carburetor which appears to be recently rebuilt.
It has a new electronic ignition using Autolite 847 sparkplugs.
It was also converted to 12 volt and most of the wiring has been changed though pretty sloppy.
I plan on using this as a project and will make changes where needed but I would like to drive it for now.

Scott
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Thank You

Welcome to the 'bolt!

I'd check a few things here. Rough idle could be as simple as an idle screw adjustment on the "B". That's the screw that is at the base of the carb facing the head. Turn it clockwise until the engine runs rough (rougher) then back it out until it smooths out.

Also, check the obvious things, firing order (distributor wiring to the plugs) and timing. Is the air cleaner element clean?

If none of these things reveal a problem I'd do a compression test next.

Hopefully there'll be some more suggestions coming soon.

brownie1,

My first check would be the valves. This would entail a compression check following recommended procedures, then a visual of the rockers and top end. Most carburetion issues involve a certain cirucit in the carburetor and appear at a idle, mid range/high range but usually not through the entire RPM range.

A vacuum leak is another suspect. Make sure the vacuum hose to the distributor is connected. If you squirt carburetor cleaner, propane or anything that will combust into the cracks and crevices around the carb base and manifold to head area you might hear the idle pickup and the engine smooth out. This indicates a vacuum leak in that area.

If the carburetor was rebuilt incorrectly it could have problems too. Sooty plugs are a sign of too much fuel. This could be a float that is set too high or a powervalve that is covered and in the 'go mode' all the time.

Lots of things to check! The compression test would be my starting point...it should pick up a hard mechanical malfunction.


Stuart

If the plugs are full of soot, maybe they are too cold. Before I would do anything that involved a lot of work, I would put in a new set of the correct heat range plugs and drive it pretty hard for several miles. Also, how does the gas smell. If it's stale, you are risking valves sticking, as well as running badly.

Check the compression . If that is not right it will never run right. Cleon