All you have to do is take the head off and fill the port with brake cleaner.(either intake or exhaust) Then look at your valves in the combustion chamber for any leaks. If so take a drill and grab the top of the with the chuck and spin the valve until it feels smooth and spin in both ways.(A small cordless drill works the best)Finally refill with brake clean and test for leaks. This worked prefect on my gy6 83cc with a ported 50cc head. Lots of compression now the valve seats are good.