I took out my 86 LT250r for a ride the other day and after riding it for about 10 minutes, suddenly it had no bottom end, and definitely wasnt pulling like it should, and had a surging idle. Also was producing more smoke than usual... just as i got back it stalled and hasnt started since. Could it be that i sheared the flywheel key that keeps the right timing? Or damaged a reed? Any ideas?
Thanks

 

It sounds like a seal went and it has an air leak (explains the surging idle) and gear oil is getting in the combustion chamber (explains the extra smoke). Check the cylinder base gasket and pray it is not the main bottom end seal between the halves.

-B