I have a john deere L120 tractor with a Briggs and Stratton 20 hp vtek twin engine. The problem i'm having is it runs good mowing for about 15 minutes till it gets hot and then it starts to sputtor and finally dies. Its helps for about a minute before it dies if i put the choke on full. I wait for a few minutes and try to start it again it will start and only run for a minute on full choke then die out again. As soon as i try to move it off full choke it dies right away. It runs great the after it completely cools off and then 10 minutes later when it heats back up it does the same thing. Any suggestions would be greatly appreciated. I put new gas and a new fuel filter on it. It has a fairly new air filter in it also.