ORIGINAL: RussianFlyer
I've found that with my TT Pro 46 engines, the needle valve housing has a tendency to loosen up and create an air leak. Double check that yours is tightly screwed in (don't strip it, just verify). The housing is the part that the high speed needle screws into. it also sandwiches the fuel nipple fitting against the carb.
I had that happen, also. Course smacking the ground repeatedely engine first didn't help. [:'(] I replaced it with a Perry Carbureator and, once I had it adjusted, never looked back. I did have to tap a bolt hole in the engine casting as the plastic carb wouldn't stay put with the dowel-with-a-bite-out-of-it retainer system.