I sold this tractor to my neighbor a few years ago. He recently mentioned an issue it has where the engine starts and runs fine but intermittently seems to start sputtering, loses power and smells rich of unburned fuel. It will do it for a little while, then snap out of it and run normal again. To me it sounds like it is losing spark on one side. If it were a valve or anything else mechanical, I believe it would be more consistent.
Just looking for some insight on possible causes. Should I be looking at the coil? Is there one or two on this engine?