Here's the plane hovering just fine on an OS .70 four stroke:
http://video1.hobbico.com/gallery/gp...021-deluxe.mpg

All this stuff you're talking about with the engine sounds like you're missing something with the tuning and setup (temperature, compression, lack of power). I don't think the problem is the plane or motor.

Go to the RCU Ratings page:
http://www.rcuniverse.com/product_gu...fm?kit_id=4630

Everyone else is happy with the 55AX. Some people are using a smaller prop (12.5x5 or something like that).