i agree either valve clearances or crappy piston rings i have bought and sold a few of these and they have useless piston rings that lose their temper and go weak.does it smoke when it was running?i can tell you that if you need a new piston and a rebore use a yamaha t80 townmate piston as this is what they use even though its a 90 its the same piston(believe me)they are a longer stroke than a t80.
adam bike doctor, May 2010