Tmoth4
Bigger carb (WT-9), better muffler, deck crankcase and machine rear of crankcase to stuff it.
Also Bowman full circle rings and CH ignition. Every thing adds a bit of power and soon you are at 7500. Prop is a MA Simitar 18x8 wood. As the engine breaks-in it gets better.

Are you sure you have the 30cc engine and not the 25cc? About the best the 25 will do is an 16x8 APC at 9000 with all the mods