He says he has a good idle, so do not change the air bleed needle at all. The airbleed needle regulates the airflow though the small hole in the front of the carb. Sounds like it is right on.

Height of the needle valve is not a problem as long as the tank position is correct with the carb (and he says it is so). I am of the opinion the hugh prop is the problem, it lugs the engine down, keeps the RPM down (but helps the idle, right?). A 10 X 6 is plenty of prop for the engine, since it is not new, maybe a tiny bit to much, maybe a 10 X 5 or a 10 X 4 would be much better.

And since it is a sleeve bearing engine, some Castor ought to be in the fuel.

Good luck,

Chip