Hi Dave,
I have a ys63 that has about 8 gallons of fuel run threw it
is it time for a new piston ring and or liner?
I am asking because the compression is definitely not what it used to be and the
valve lash is @ spec
power master 20/20 is all that has been used and I don't see any carbon deposits
in the combustion chamber so I am assuming the valves are seating properly
Thanks for your time
Frank

Might be a buildup on the valves that is causing them to hang open. You can use some fuel to check for valve leakage. If it blows bubbles, they are leaking. Check both intake and exhaust.