I recently bought a tigermoth biplane and will be running a os .61 fx, however unlike my last plane ( a trainer) the engine in this one is mounted upside down. My problem is I am trying to break in the motor and am following the manual for needle turns etc. But I can't turn over the motor when its upside down, its like its got too much fuel in the chamber and is locked up, but when I turn the plane upside down so the motor is upright I can get the engine to run like a top. How or what am I doing wrong since i am following all the directions.

OS # 8 gloplug,
15% N 20 % oil fuel

Thanks Ickleboggle