I ended up replacing the fuel pump on my '46 (after it completely crapped out). Thinking back, there were warnings.
If everything else is where it should be, but you are getting variation in engine RPM's above idle at any particular throttle setting, then it sounds like variable fuel delivery or vacuum leakage, or a combination thereof.
Fuel pump can be a easy culprit. If you are gravity feeding the carburetor during testing, you may not have enough fuel delivery to the carb at continuous engine RPM's greater than idle.
If the fuel pump is old, sat for years, and worked when you parked it, that could be the culprit.
Golly, it's fun to trouble-shoot from miles away, and it don't cost much either.
Drive that ol' '41 up to Jarrell someday.
