I've got a farmall 400, I dont run it much. Mostly sits in the barn waiting to be restored. But when I do run it, I am constantly having to replace or clean the plugs. They are always fouling up after a few hours of use (25-50 hrs). I've been asking around and I was told its from the carb running too rich. So I plan on adjusting, but not sure on how much adjustment it needs. How much adjustment are we talking? Or, am I off base completely with the adjustment? Any advice?