How do you check for compression on a gas engine and what do you need to do it? Thanks...

If the engine uses 14mm spark plugs you can get a cheap compression tester at an auto supply store..Crank it with a starter...For a reference and G62 will show about 115 PSI with the cylinder dry and about 150PSI if you pour a little motor oil in the spark plug hole first...
Flipping by hand will show lower numbers...
If the engine runs well who cares ?

Well it is a McCulloch 28cc weedwacker engine that I am about to convert for RC use and want to make sure it is ok before I spend the time to do it. It did run prior, but it didn't feel like it had as much power as it should have, at least that is the way I felt it. When I took off the back plate to expose the piston area and turned it over by hand, I heard air seaping by the piston, not sure if this is right or not. Does anyone know what kind of compression I should be getting with this engine? Thanks...

It's not physically possible to completely seal the compression, so most engines will sound like that when turned over...Check the conversion forum, someone there might know..

OK, Thanks...