In Reply to: 51 8N Spittin & Sputterin posted by Steve in MO on July 22, 2018 at 03:42:35:
sitting that long, I would not rule out the mechanical advance in the distributor sticking or maybe some valves sticking.
The Idle rpm is not a big problem, it is probably sucking air in around the throttle butterfly shaft. 400 is for show tractors, mine seldom run at an idle and one is about 600 and the other maybe 500.
I don't think the governor is your problem, but disconnect the rod going to the carb and run it up by hand and see what happens, bet it runs the same.
on the carb adjust, I like to start at 2 1/2 turns out on main jet and with it running full throttle after warming up, I adjust it in until it just starts to falter, then back out 1/4 turn or so. fine tune from there under load.