I'm having the very same problems with my Aviastar .46 purchased in September. I think the air leak is a loose fit
between the carb barrel and body. Both needles are VERY critical, hard to tune perfectly. This engine also likes hot plugs.
Mine transitions a lot better now, but one click either way on the high speed needle could mean four cycling rich or a lean run.
I still can't stop the engine by shutting down the carb. Mine also Knocks at cold startup. I think it's a tight TDC pinch, a little more breakin time will tell.
Good luck rduff55, let me know what you find.

David