Sounds like the governor is not set correctly. There should be a lock nut on the governor arm at the swivel point if it is like most motors, I'm not familiar with the Honda's, that you loosen off, set the throttle butterfly to full open and turn the governor, usually by a screwdriver slot in it, to the full clockwise position and tighten off the lock nut. When the engine is not running the throttle butterfly should be full open. The governor operates to close it down as revs increase. Someone more familiar with the Honda's will probably be able to give you more info.
