how do i check compression so that i can see if the valve seating is ok?

 

Take spark plug out. Thread in compression tester gauge.(available at local autoparts store for around $20). Hold throttle wide open and crank over or pull start for a bout 5 seconds or so. Read gauge.

P.S. make sure the threads on the compression gauge do not exceed the length of the sparkplug threads or you could damage the piston.