I saw this same thing happen to a guy last week. He filled his plane with fuel & didn't dissconnect the pressure line from the muffler or tilt the plane up when filling it. By the time the fuel ran out of the end of the muffler the cylinder was also full of fuel & he couldn't turn it over. He had to tilt the plane up & lean it over to drain the fuel out of the cylinder into the muffler & out of the muffler. Then had to turn the engine over by hand to finish working the fuel through it. Then it cranked & ran fine. The engine was an os91fx.

Gil