Your low needle setting seems about right, but you never mentioned what happens when you open the high needle. You did say that you have been using gas engines for some time so I am assuming that you are using the correct method to tune the carb. If in doubt, start by opening both needles say 1.5 turn and tune the high needle first for max rpm. Then lean the low needle slowly until the engine dies when the throttle is briskly opened from idle to say 3/4 throttle. Then sowly richen the low needle in very small amounts until the engine transitions cleanly then readjust the high needle for max rpm and finally reduce by 200 rpm for flying. Or maybe it's time to give the carb a rebuild.

Karol