Folks, like any 2-stroke bike, the TYs are sensitive to carbon build up in the exhaust. When there is too much, it affects the exhaust pressure waves which affects the scavenging process and may make the piston rattle if not corrected. The TY sounds rattlier than others because it is air-cooled and hence no water jacket to muffle sound. Burn it out. It won't cost you much at all and you'll find the need for engine o'haul may not really be necessary.