onan 5500 generator problems

generator driving me nuts. always well maintained, but now having issues. flash code not helping me. replaced fuel and filters and added seafoam to the tank. it will run for 10 minutes, sometimes up to 1 hour with smooth idle and then just shut off. it seems like something is getting hot and opening a contact. it will not start back up for about 15 minutes and then same thing. I don't think its a fuel pump or carb issue. seems more like coil or internal short. can anyone help me please. p.s. bought Honda 2000 backup genny for now seemed like cheaper fix.