It is possible that this engine does not have a gas ported piston. Without it, the symptoms you describe are quite possible.

Your best bet is to send the engine so that service can verify if it has the piston mod.

Here is the address:

YS Service
1295 Industrial Court
Gardnerville, NV 89410

Phone 775 782 4562

Sorry for the hassle, but it will be easier in the long haul to let us see what the problem is.

Dave