Keith:

The valves would have to be pretty far off to cause that much rpm loss, but it's possible. Valve adjustment is not a warranty item, though, you should check that before returning the engine for checking/service.

If you didn't get the owner's manual with the engine it's available for download from Horizon. It is not as clear on the operation as it could be, but with a second or third reading it will become clear to you.

Bill.