Hi!
The first thing to do is to replace the ballbearings with new Swiss,WIB C4 race ballbearings.
Second to raise the head some (0.1mm-0,2mm) and use more nitro, like 25-40% and a colder plug.
Third ...to use a tuned pipe...Forth...to raise the exhaust timing (file away 0.5-0.7mm mm at the top of the exhaust opening in the cylinder using a diamond file in Dremel).

Fifth...buy a better engine to start with... like a Nelson or Jett and forget about what I said above.

Regards!
Jan K
Sweden