[Oak]

Did you pull the carb apart and clean it? The diodes are there so one circuit doesn't back feed the other. The start circuit goes through the pto switch, brake switch and then energizes the fuel solenoid. Once it's running the fuel solenoid is powered through the seat switch unless the brake is locked on (pto must be off). With all the crappy gas today I think your problem is the fuel solenoid or other passages in the carb. I would pull it apart and clean it good with cleaner and use compressed air to blow it clean. I had the same problem with my Kubota. The solenoid is a plunger that shuts the fuel off to the carb and kills the engine. If you are choking it to keep it running then it's not getting enough fuel. Good luck and keep us posted.