ORIGINAL: Artisan
Some carbon build-up is normal and acceptable. It is also unavoidable. The engine does not need to be pristinely clean in order to run properly/healthy.
As others have mentioned, the only way to completely clean the engine will require that you perform unnecessary maintenance on the engine. Honing the cylinder for a new ring(s) wears the cylinder and risks damaging the cylinder - all for nothing.
Run your engine with a normally leaned mixture and stop worrying about a little carbon. If it really bothers you, some folks are running Bel-Ray two-stroke oil, which they claim eliminates carbon build-up. At $50 a gallon, it better do something different. <G>
Ive been running 80:1 Amsoil but since I have to mail-order it costs even more than the Bel-Ray..I can now get the Bel Ray local and I just mixed a gallon up to try it..I guess then Ill leave the engine alone since it runs perfect..Thanks