I had a similar experience. When I flew glow I flew with an OS .61 2-stroke, an OS .91 4-stroke, and an OS .75 AX 2-stroke. All of those motors provided reliable power but when I replaced them with AXI 4120/14 and AXI 4120/18...........it ran circles around the OS engines. It was clean and fit into the cowl with no cutouts for a cylinder head or muffler. But I'm off-topic - sorry.