aspeed

You can always take out the carb. completely and just put in a needle valve in one side of the mounting hole an plug the other hole.  You would want a shutoff for a "throttle".  You can always shim the liner up .020" at a time and machine off the same amount from the top of the liner to experiment with higher powerbands and a pipe. (and still go back to stock.)  Radiusing  the rod to a teardrop shape and smoothing or polishing (almost), gives about 300 rpm and doesn't  adversely  affect the life of the motor if moderately done and not revved too crazy.  Lightening the piston from the inside can get a few more revs and not hurt the life either. I wouldn't port the inside of an OS because of the lousy plating.  The crank closing time could be delayed a bit for the higher revs to unload a bit in the air.  It cannot be reversed if you go too far though.  The turbo crank thing may help a bit but I couldn't measure the difference on a couple of .15's that I tried. These should give 1 to 2 thousand rpm and a pipe maybe another couple.  (or no muffler if there are no neighbors.  To save weight for a combat or free flight you could grind off the muffler mounting tabs but then there is no return to a muffler)  I am sure there are other ideas that I would like to hear as well.