Thanks, Ed. I've used an OS #8 for the last four attempts.

The engine is at least 15 years old, maybe older. I got it second hand. I have no idea what the previous owner subjected it to. I do know he was the type that went through engines a lot faster than anyone else at the field, so I guess he damaged it somehow. It may have even been crashed.

Here's the thing. It starts out sounding halfway normal for about the first 30 seconds or so. The longer it runs the more erratic and rough it becomes. Even at a very rich setting - and I mean rich - the head still gets hotter than any of my other OS engines.

All of my other FPs run flawlessly. I've never had a bit of trouble with any of them. Something is mechanically wrong with this one. If it was a needle setting or fuel system issue it would have been solved by now.