sounds like a stuck fuel rack. restricting most of the air will slow it down and cause tons of smoke, but remember a combustion ignition engine will run at incredibly low a/f ratios..
Tractors that sit should have the fuel tanks kept as full as possible to sisplace air in the tank( which allows water in) Installation of a f/w seperator filter will help, along with treating the fuel with your favorite lubricity additive. My personal favorite is 2 stroke engine oil, cheap and effective.