Possibly a lean condition created by vacuum leak(s).I use carb spray while running and make short shots at critical areas, those related to manifold vacuum.
Anything between the base of the carb and head.
The idle rpm will change if you hit a leak, usually stumbles a little.
You'd be surprised how many you may find with a hand-held tach that you may not notice by ear.
Keep spray from carb throat and just small, short sprays.
2 cents
RD
