Terry, heres another head scratcher. I have a CA Allis-Chalmers that I cut hay with. Last year I had trouble with it stalling out. Let it set for a few minutes and it would run again. Maybe a minute, maybe 5 or 10. When I had ran it out of gas once I left the cap off while I walked back to get a can of gas. While I was gone a bumble bee thought that open tank was the place to be and once inside was overcome by the fumes. Every so often that bee sloshing around would clog the fuel outlet and starve the engine for fuel. You might look in your tank for something floating around in there choking off fuel flow. Another thought is where is the float pivot in relationship to the back of the tractor? It could be that if its toward the front the engine would have to use more fuel from the bowl before the float could drop and let more fuel in when the wheels were off the pavement.