The newly rebuilt 1954 235 with W-1 in my 41 does this once in a while. I learned to employ the hot start method Jon referenced pressing the accelerator just very slightly while starting and it solved the issue. I think I do it automatically now as I don't think about it any longer. It was an intermittent issue that had much to do with the engine temperature, air temperature, and humidity. You will figure out what technique your particular engine/carburetor needs.
