I'm not new to 2 stroke OS engines both helicopter and airplane but this one has me puzzled. This engine was installed in a Raptor SE that I traded for a fixed wing model. The owner of the helicopter said it had about a gallon of Power Master 30% nitro 23% oil mix. From a visual inspection the airframe and engine looked pristine. My mistake was I did not request the helicopter be flown. If the engine ran like it does now I would never made the trade. The carburetor installed is the 40E model. This is what I got for my mistake. The engine behaves like it is it is missing or not firing on all cylinders. Never have I seen a 2 cycle engine do this. At idle it is shakes rattles and rolls. It is not lean or rich and in forward flight above 66% throttle setting it appears to be runing fine. Transitioning back into a hover it's okay. The problem comes back in hover and idling only.