Hello! I'm getting crazy not being able to drive my Z50J 73cc The problem is i adjust the cam chain so it lines up with the dot and the flywheel perfectly. After 10 minutes driving it starts going slowl and i feels it has no power, because the cam chain is somehow jumping teeth on the cam sprocket That means the piston starts hitting the valves. I've tried replacing the cam chain and guides with the 50cc ones, still same problem. I'm thinking it could be a problem with the tensioner spring or both the cam chains are worn? Anyone else had any problem like this? Thanks for help!