Engines that run at a very constant rpms have carbon build up issues. This is due to their never changing combustion chamber turbulence patterns. Engines that have ever changing rpm ranges don't develop these issues. This is the reason that our Onans require having the heads pulled off for carbon deposit removal. It's required after so many hours of operation. I don't remember that number of hours right now. So to keep your Onan operating properly. It's a very simple task to do. Anyone can do it. And I mean anyone. Bob Dunahugh Member GMCMI