This is a very old thread but I thought I would mention I was looking for this info on backflipping the four strokes. I broke two props starting my OS FS 120 with a stout wooden chicken stick as the engine kicked back CW. The thin trailing edge of the prop was crushed on one 16x6 Zinger prop and then a 18.8 broke at the shaft. I need to see if I can do this back flip start next time I get the engine set up on my test stand, before getting it back into the Sig 1/4 Scale Cub it came from. In the meantime I picked up a torqmaster 180 starter and I will go with adding a spinner to use the starter. I prefer to hand flip, though - less encumbrance of big 12v battery and big ol' starter. Travel light.