My reliable 80 720 started misbehaving. It got to where I would have to rev it way up 7000 ish and slowly let the clutch out to limp it home two blocks. My son came over and (he has better eyesight than me) discovered a freaking 12mm nut in the bottom of the secondary chamber!!! Not the side with the choke on it. I have no idea how this bolt got in there.
With the nut removed, the idle returned to normal (it was high) and it revved normal, so I decided to give it a test drive. Result: Fail. It still did the same thing and I had to push it home (1 block).
Full disclosure. When the truck was progressively losing power I blasted the carb (with motor running) with choke and carb cleaner.
I appreciate any help with this bizarre problem.