I'm trying to get a 1250 to stay running. Starts easily enough, but shuts down after it gets hot. Restarts immediately, but then shuts down again in about 15 seconds. I've rebuilt the carb, and then even swapped the carb, coil, condenser and plug wire with those from my 108 (which runs fine). Tried fresh gas, new fuel filter, and problem persists.
Coil gets very hot, as does the one I substituted from the 108. On first startup from cold, it runs for several minutes. As it gets hotter, the run time decreases, so it seems temperature related.
When it quits, it's with several loud backfires, so I don't think it's fuel starvation.
Plug appears sooty, but not oily, although this 301 is smoking and leaking. Adjusting carb main mixture 1/4 turn either way has no effect on how long it runs before it chokes down again. I believe carb is adjusted correctly- idles very smoothly, and runs smoothly- until the shutdown occurs.
Any suggestions will be greatly appreciated.