Clancy,
Please, please don't stand in front of the engine while it's running. Four strokes often kick back, especially when new, and will throw a prop completely off the prop shaft. This can also happen when you're starting it, but at least the engine isn't running. Until the engine is broken in, the valves seated and the carb adjusted, be careful! I've seen some very close calls, including myself, at the R/C field. Also, be aware that the larger mass vibration can loosen anything in you're mounting rig that's not secure (i.e. C-clamps). Have fun, they are great engines, but very strong.
Paul