Troy built mower with a Kohler 20 hp one cyc. gas engine. Starts, runs for about one minute, the stalls, as though running out of fuel. No backfire, exterior is clean, Suspected oil sensor, but engine does not have one. Changed oil. Cleaned out fuel tank, replaced fuel line, filter, carb,, coil, electric ignition module, and spark plug. I call this the shotgun method, replace everything, one at a time, Tried hot wiring carb coil (shut off on bottom of bowl). Makes me say "Hummmmmm"