It's probably not broken in yet if it was new or you put in a new piston ring. You need to change the carb however. The stock carb is very tiny. A carb with an 11mm venturi would be best. Also, do you have a nice free breathing muffler on it?

I'm going to get mine out and run it some more to break it in today, but first run it turned an 18 x 6 Power Point at 7000. I'm hoping it comes up to at least 7500 on that prop, and according to the performance others report, it should do that if not more.

AV8TOR