This ski came to my shop for diagnose lack of engine power. We found few cause of problem. At first YPVS valves problem.
This motor had been top rebuild by this customer.
They fitted valves up side down.
This is correct way to fit.
Few exhaust gaskets didn't replace as re-used because water leaked to exhaust and damaged pistons.
This metal gasket are not re-useable, some people confuse as it can be re-use. Gasket are have to replace. 
Brand new pistons are damaged,,,,,,,
