ORIGINAL: planepounder
I use an electric start as this is an older mag engine that is hard if not impossible to hand start. Since prop position for starting is not critical, I would like to place it for best engine balance. I think I remember that the prop lines up with the rod @ TDC, but I am not sure.
Engine balance is influenced by the prop position. If the prop is in line with the unbalance of the total engine, it will lessen the motion along the engine axis. (like the balance stave of a chord dancer) The trick is to find out what position is best. For a two blade prop I would try out three prop positions first, each 30° different to each other. Then change position either way 15°, which should get you extremely close.
With a three blade prop, the effect is quite a bit less pronounced, so much even as to not to bother.