Tuning issue. Did you have someone at your club help you? Sounds too rich to me. How many turns out is your needle? Are you sure you're counting 'full' turns?

You should start from scratch; while the engine is off, close the needle all the way (don't crank on it, just until it stops turning) then open two and a half 'full' turns (to the left) and start the engine. This would be a very rich position. Turn the needle SLOWLY to the right, a few clicks at a time (make sure you realize what a click is, a guy at my field kept turning like a quarter turn at a time. Literally one click) until you get to peak RPM, or at least what sounds like a plateau in the increasing of the RPM, then richen 4 clicks or so. Check by pinching the fuel line to the carb; a brief pinch and let go. The engine should speed up when you pinch the line. It it wants to quit, you are too lean.

How many tanks of fuel have been through this engine, is it pretty new?

Also have you touched the idle mixture screw?