I had a 120 OS in mine, there was plenty of power for it and it balanced exactly as it said in the manual. Everything appeared to be fine. After the initial flight we tried mixing in a few bits and pieces, aileron and rudder etc, all the normal things. Don't know why it performed badly but it did. Even had a couple of instructors have a go at it and they felt very uncomfortable with it. Was a shame because it looked so pretty.