I have a buddy who has an 06 650, I understand this is a Kawasaki engine. He has the valves adjusted and it runs for 4 or 5 hours then will not start again. Has them adjusted and goes through it all again. What do u think the issue could be? Valve seat or valve spring weak? Does this thing have a hydraulic cam chain adjuster?

 

pull the valve cover and check the cam lobe make sure they are not wearing flat. I had one do this to me. The motor was back firing alot also through the exhaust.