hello, I fly mine with two shims under the enginemount on the left side to get some right trust, still have to trim in a little right rudder. I used to run a os 91 fx but have recently put in a sc 91 fourbanger. I use apc 14/4 w on both engines. flyes great on both, but you can`t beat the sound of the 4 stroke even though it has less power to pull out of hover, but it is sufficient. I have max deflections on all moving surfaces and the cg way back. when I fly inverted on half trottle I must give a little down elevator or it climbs.