take the muffler off and get the tower hobbies muffler, 300 rpm. [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXJB16&P=Z]tower muffler[/link]

could remove the head and take out the shim, increases compression but can reduce the engine life.

if your not worried about ruining the engine you can take the sleeve out and polish the exhaust ports.