VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc 1940 216 only runs at high rpm

My 1938 truck has a 1940 216 engine with a 1938 W1 carb. I have replaced the head gasket, exhaust and intake manifold gaskets. I have put carb kit in it, but not recently and replace base gasket. I also cleaned the gas tank and fuel lines. I have replaced the fuel pump. Looks like good flow to carb. I placed a new in line glass fuel filter before the carb and gas looks clean. I replaced the points, condenser, rotor , plug wires, coil and battery.
This engine starts easily, but only runs at high rpm. It runs pretty smooth at high rpm. I have to full choke to get it started or dump gas down its throat. It won't stay running at idle. If I leave at idle, I have to choke almost completely to get it to keep running. If I can keep it running with choke, it runs at high rpm only but won't idle. If I open the throttle it runs at high rpm and I can slowly open choke butterfly to full open. If I back off on the throttle it dies. I thought it might b a big vacuum leak so I sprayed wd 40 at the carb base and around the intake manifold gaskets, but that did not seem to make a difference.
The reason I replaced all the gaskets is because the intake valves stuck and I had to remove the head. I could not see anything wrong with the head off. This engine ran like this before I took the head off to unstick the valves.
This engine has never run correctly since I've owned it. I have limited time for it, so it has taken me this long to get this far. I am determined to get this thing running, but I need professional help now (and not just psychological).
The next thing I thought I'd try is to plug the vacuum advance tube and see what happens.
Is there a way to check the vacuum advance dash pot at the distributor? It seems to hold against my finger for about 3-4 seconds before it slowly lets go. Could this b the problem? Something else?

Thank you

Its not the vacuum advane as it is not "working" at idle speed.
Also seeing it holds vacuum it would be OK.
I suspect that if it isn't a vacuum leak it has a problem in the idle circuit in the carburetor or in the tube that sits at an angle and sucks gas out of the carb. bowl and lower speeds. See diagram in shop manual..... or a cracked insulator between the carb. and manifold.

I'm far from an expert but my first thought was the low-speed/idle jet in your carb is clogged. This happened to me right after a complete carb rebuild. Some little piece of something got in there. Had to remove the carb and clean the jet again and then everything ran fine.

Many years ago I had a 47 Chevy W-1 carb. had same problem, Old time Mechanic told me to take Idle jet out and use air gun to clear passage worked Idled and ran like new.That was 1953.

Not to long ago my all stock 1936 Chevy would not idle. To keep it running I had to give it throttle but would constantly die if I was not quick enough. It was so bad I could not drive it at all.Finally I took the low speed jet out of the carburetor and cleaned it. Now the problem is gone and it idles like it use to. Your problem sounds very similar. I am not sure of the specifics of your carburetor but it seems to be something to do with the low speed jet.

Notice that you are replying to a problem posted three years ago. I would think it has been resolved by now.

Also there is an easier way to blow out the low speed jet without even touching the carburetor.

The low speed jet is in play at low speed only and if it is plugged-up the engine will run fien over 1000 rpm.

Ha! No, I didn't even notice. Just shows that one shouldn't cruise the forums before the coffee is ready.