A friend of mine learning to fly got a MDS-40 on a trainer combo. For two months we tried to get it to run for more than 1 minute with little or no success. We tried different carbs, sealing the carb to the crankcase, different glow plugs, fuel sleeve orientation, fuel line leakage, fuel draw to tank location with no success at all. We sent it back for service with the same symptums as described and was told that there was nothing wrong with the engine. After reinstalling the engine in the plane the problems existed. He bought a O.S. 46 and installed it in the plane and right out of the box the O.S. performed flawlessly for two years now. MDS is a sour subject. We never looked back.