The exhaust valves are their downfall they burn out and go a bit of a funny shape on the head,so as bb says it seems like its low on comp and this may well be the problem.
adam bike doctor, April 2010
I would suggest your compression is low? how is it to kick over is it really easy or is there a pressure when you push against it. c90 engines are pretty bomb proof. When did you check or change your oil last?
