My 518-H runs and mows for about 15 minutes then stalls. It'll rest for 10, then run for 15 and stall. The oil level is right, air cleaner is clear and it has new spark plugs. Sounds like overheating, but it isn't really very hot to the touch. Onan twin. I brought it to the CT Onan dealer and he couldn't fix it, but frankly, they work on generators all day and I don't think they wanted to bother. Any ideas?