Hi, everyone I'm a farmer from Wisconsin and I run a horse boarding facility. I've been having a issue for some trouble with my 311b. It's like clock work once it warms up the tractor cuts out and only wants to run on choke. I went threw the zenith carb with a fine tooth comb, a half dozen times or so and it never made a differnce. So I changed the fuel filter, tried running with the gas cap off, changed the old fuel line, to a hard line just in case I was getting crimping, got rid of the inline filter that had been installed and am now just using a sediment bowl which I've never had anything collect in. And finally I broke down and ordered a reman marvel carb and it still acts up. I'm thinking of pulling the tank off because this screams a fuel issue to me but I am honestly lost. Tried replacing the coil as well no luck thinking it may be a ignition issue, and pulled all the plugs and they look great. Oh and I sprayed starting fluid around the intake and it made a very very small increase in rpms but nothing I can imagine that would make a difference. I do know the head gasket is going out and I'm thinking that may have something to do with it. Any suggestions would be appreciated, I'm by no means a master mechanic and this thing is twice my age so I've never really been around older case tractors much. I really appreciate everyone's time. Mike