JD x530 with just 60 hours and a full tank of good fuel and no previous problems. Works at idle and when you engage the mower and mow for about 10 minutes or more it will flutter and die. I have replaced the fuel pump with a brand new briggs pump from Deere. I have put on a gravity feed small lawnmower tank and connected to the inlet side of the NEW fuel pump same thing. The only way I can keep it running is to hook the gravity tank to the carb directly. Is it possible that the pump is not pulling enough vacuum under mowing load. Open for ideas???????