Motorcycle Repair: yamaha pw 50, yamaha pw 50, exhaust gasket

Question
I am having to bore the cylinder one size over and I need to know what the piston to cylinder wall clerance should be.
Also why does the pw 50 exhaust gasket have such a small hole in the center of the gasket ??

Answer
21136-001 GASKET,EXST PIPE
(UNRESTRICTED)
order the above part....the ex. gasket you have is the restricted one, hence the small hole.
the rule of thumb for the piston to wall clearance is .001" per inch of bore. When you take the cylinder to be bored tell them that you want the clearance on the snug side. They break in and run better that way. Be careful with break in ride easy for 10-15 minutes and cool for 20-45 minutres for a few cycles... Heat and cool with out beating the poor thing up is best for break in.
Good luck.