I have a 5FG with the same motor and mine is doing the same thing. Some days it runs ok, other days it runs like crap. I rebuilt the regulator and have taken the carb and gov. apart 2-3 times and cleaned it out every way possible. It was pretty clean. Its only got 4xxx hours on it. (1998)

I dont think its the valves, it wasnt a gradual issues, it just happened out of no where.