I have a John Deere LA 115 with a Briggs & Stratton 19.5 motor 31P677, I have been working with this problem for about two weeks. I was cutting grass and it stalled and then stopped. This is what I have done so far, I checked the valves and adjusted to specs, new carb, new fuel filter, new plug, new fuel pump, and now it starts and runs for about five minutes then sputters and dies. What next, I just can't seem to figure this out, any suggestions?