A common wear point on 2-stroke engines, especially engines run a little lean and hot, is at the wristpin. The small end of the connecting rod and sometimes the piston pin bores will get wallowed out. This is one of many causes of black gunk coming out of your muffler. If I am not mistaken, I think the Evolution engines do not have a bushing in the small end of the connecting rod. Someone please correct me if I'm wrong.