The Stovebolt Site Forums The Shop Area Engine Shop Carburetor adjustment

I rebuilt my Rochester B, and my truck ('53 3100 w/a '55 235) starts, warms up, and runs fine until I attempt to back off the choke, at which point it dies. As long as the choke is activated, the engine runs great. Do I have it adjusted too lean? And if so, how to I adjust the carb to create a richer mixture? Thanks-Lee

http://chevy.oldcarmanualproject.com/carb/Rochester/index.htm
This may help

Check to make sure that you have the proper carburetor base gasket where it meets the intake manifold. There is a hole in the intake manifold which may be covered up by the wrong gasket.
Carl

Yeah, I had to cut a hole in the gasket to keep that channel open......

Float set too low

Mixture screw should be 1 1/2 to 2 turns out from a seated position. If that doesn't help, then you have dirt somewhere or the float is really low causing a lean conditions. How did it run before the overhaul? Do not adjust timing till you get the carb running as least as good as it did before cleaning, you don't want two problems at the same time.

Joe

Oh dang! I set it according to the specs and used a micrometer....Not getting enough fuel????

I've got the mixture screw at 1 1/2 turns. I am not sure how it ran before I got it. According to the PO, "Fine!" But when it came off the transport trailer, it started up and a minute later died; carb completely choked down by rust that must have dislodged on the trip from Kentucky to Texas. I'll try the mixture screw....and pray THAT'S the answer..... easy fix....(I'm usually not that lucky, tho).... Thanks. -Lee

It's absolutely amazing what little gremlins will show up after a trailer ride of a few hundred miles. Unfortunately these carburetors can be a touch problematic. Probably something simple that you will slap your forehead and say "why didn't I think of that" when you find it. Take all of our suggestions in the spirit they are given, after all we are here to help not belittle you or put down your abilities as a mechanic.

Also check the fuel flow, crude could be clogging the fuel outlet at the tank.

Good catch on the gasket hole! Lots of people miss that one.
With that ruled out, I would suspect an accumulation of varnish in the idle circuits. What is the history of the gas tank?
The volatiles in ethanol gas is an excellent solvent for the many years of accumulated deposits on the walls of the tank which would normally have stayed in place. Now they may have migrated into the carburetor where it is now accumulated, plugging the tiny holes.
Carl

any chance of a vacuum leak ?
my advice may not be to good though, my 52 with a 235 had no choke, drove it for many yrs, pat the foot feed about 3 times, hit the stomp starter and she was purring like a kitten.. a few times in real freezing weather I played with it a little more but not much.......what do I know. I just not to over think it

[quote=52Carl What is the history of the gas tank?

Carl [/quote]
I cleaned the tank w nuts and bolts and sealed it (POR15). The fuel lines are new, and the pump is new. I soaked the carb for 24 hrs and used my compressor to clean out all the passages. Installed a carb kit. All works great. I just cannot turn off the choke without killing the engine. I won't be home until tomorrow. So I'll get busy on it then. Thanks for all the info! You guys are the BEST!!!!

Get out your propane torch and open the valve slightly w/o lighting it. Start the engine and run the unlit torch around the carb slowly. If the engine speeds up you found a vacuum leak. While your at it you might as well run it around the intake ports and manifold.

Very interesting..... You guys are so smart!!!!!Thanks!