Does it have an oil bath air cleaner? If so, water may be in the oil. When the engine is running this can be drawn up into the mesh and freeze blocking off the air. Starting fluid will not eliminate this condition. To check remove the hose between the air cleaner and manifold and see if it will run. To solve, pull the oil cup off the air cleaner, heat the cleaner above freezing to get the ice to thaw and run out, and then clean the cup and put in new oil.
My Allis B would do the same thing.