I prefer to break mine in on a stand mounted sideways. That way you don't have to worry about getting the glow plug wet if you should go rich (as you should on break-in), and the carb has easy draw for fuel (instead of drawing the mixture up hill as is the case with four-strokes mounted upright). When you invert the engine, you will likely have to readjust the carb (especially the low speed mixture), but you don't want to worry about that until after the engine is broken in enough to fly- then you can set it for optimum inverted operation.