Sounds like you're not getting vacuum to draw the propane into the carberator. Did you check the compression after you did the head gasket just to make sure you have correct compression. Also when cranking if you put your hand over the carberator hole do you feel it trying to draw on your hand if not l would think that your not getting vacuum. Does it have electric fuel lock or vacuum. Also check make sure governed plate is not stuck closed.and that the carberator diaphragm is not stuck down in the carberator.