I have a os 55 ax mounted on its side on a profile aircraft. the fuel tank it mounted on the otherside of the fuselage at the same point as the engine. the engine runs great when right side up and when verticle it can climb for unlimited verticle. Engine stalls when plane flying inverted for 5 seconds or longer. engine will stall while converting a blender to inverted flat spin. keep in mind since the engine is mounted sideways that the engine itslef is not inverted. while draining tank I can get every drop out of tank, trying to figure out why it stalls? Running 2 clicks richer or leaner does not help.