The Stovebolt Site Forums The Shop Area Engine Shop Carb problem

my 40 chevy pickup will only run with the choke half opened. open it completely and it dies immediately. Dusty has suggested a blockage in the carb somewhere. any other suggestions?

thanks, Ken

You have a vacuum leak at the base of the carb, the intake manifold orcracked vacuum line going to the distributor.

Is this at all engine RPM, or just at idle? Have you done the standard check of compression, ignition, and idle vacuum readings?

Generally, if the engine will idle with the choke, but die without, then carburetor blockage; but other factors can cause this.

Generally, if the engine will not idle at normal idle speed, suspect the vacuum leak.

Jon.

Hmmm ,, right ,, I didn't think of the vaccuum leak Luke ,, a good option to look for .

ok guys, I'm still puzzled...checked for vaccum leaks, bought another carb kit and rebuilt it my self, a friend came over and checked the compression and valve lash...all good. still only runs with choke pulled out about 1/3 of the way. also, when the motor gets warm, and you shut if off, can't get it to crank until it cools off. I did a search on here and found where someone said to pull the dipstick and see if the oil smells gassy. I did and it does. If the fuel pump is bad and dumping gas into the oil could this be why it's hard to start and possibly the answer to my other problem of not running without the choke? Even though there seems to be enough gas going to the carb...inline fuel filter is 3/4 of the way full.
thanks, Ken

Potential fuel in the sump sounds a little dangerous ,, I would pluck that fuel pump off and check the diaphram ,, plan on putting a kit in it .

I would replace the pump, at least that is what I did when mine went bad. New pump was only $2 more then a kit.
How did you check and verify that there are no vacuum leaks?

Keep us posted

I'm a little suspicious about the fact that it "won’t crank" until it cools off. Something like that would make me wonder if there was an electrical problem in addition to the fuel problem. If it won't even crank, I wonder if some electrical connection is opening when it heats up.

About the fuel problem . . . I don’t know about the older trucks, but my '53 has a spring just below the carb. This spring changes the flow of the exhaust gases in the exhaust manifold as the engine warms. If your truck has one of these is it missing or broken or overly tight. My factory repair manual says that this could be a cause of poor running or low gas mileage.