The 15 hp Kawasaki on my Gravely 34Z is acting up. It runs fine, then feels like it is running out of gas after about 15 minutes. I've changed the fuel filter and fuel pump, but it's still stalling. If I let it sit for a minute or two it runs fine again. I'm thinking it may be a bad coil that acts up when it heats up, or maybe a bad fuel line, but I may be way off base. I have the same motor on my Ferris walk-behind, and it has never done anything like this. Has anyone else had this problem?