BKF:

I just flew my Roo last weekend with a P-80. What do you have between the mount and the turbine? I used a 1/8" piece of balsa, with holes in it to allow it to sit flat over the bracket mounting screws, then glued a piece of 1/64" ply on the top of the balsa (closest part to the engine). I then added washers to the rear of the mount to give it the downthrust that the manual asks for.

Thanks