Yes, sounds like a classic air leak symptom...  but also check to make sure carb slide isn't sticking.  Should close with a "thunk".

Sounds more like slide sticking open from carb being over-tightened for 50 years. Just back the nuts off a couple of flats each side & open & close the throttle fully to see if it stick on full song. Fat Oring in the carb flange can cause that but if not that then just lots of tightening over the years. Might be a good idea to leave the decomp in place for a bit as it'll save the day at moments like this & i hadn't thought of that initially.