I have removed the undercarriage so that I can use the tractor just for pulling. It will start if I use starter fluid in the carb, but will not keep running, is this possibly a safety switch issue?

Need a little more info about your tractor. But if you have a Briggs and Stratton, engine the problem is likely the electronic fuel shut off valve on the carburetor float bowl. Safety switches are almost always ignition interrupters.