ORIGINAL: lfinney

the easiest thing to do is as you have done, a simple cleanup, but you could raise exhaust timing to 168-172 degrees and gains some added performance as well, the old adage about polishing is just that , as it was truth for low rpm car engines IE 0-5000 rpm , which has no bearing on our rpm range for these engines. the carb as it is is a major bottle neck, so enlarging the carb throat to around 10-1.5 MM will make a large difference. OS engines heli engines 50 size and up use 10-11 mm throat diameters without the use of pumps, but use muffler pressure, heli engines usually run in the 16-20k rpm range with standard gearing.. which is right where most guys here are trying to achieve