All I will add is, it is not the carburetor. "Its never the carburetor." Check the points and associated ignition parts as Martin recommends.
Even if it turns out to be the carburetor, they are difficult to diagnose and taking them apart is tedious. Save that for last when troubleshooting engine problems. You need to check everything else which can cause an engine to not run right first.
I cannot tell you how many times that I have not listened to my own advice, and tore the carburetor apart for no good reason, only to end up finding that the real issue was caused by an easy to test component unrelated to the carburetor.
It will help if you can describe more specifically what the engine sound like when it fails to do what it is supposed to.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission