Remove the gas tank of the John Deere and slide the siphon hose into the tank.
Use the hand pump on the end of the siphon hose to drain out all of the bad gasoline from the gas tank.
Refill the gas tank with new, fresh gasoline and the fuel additive. Follow the directions on the bottle of fuel additive to make sure too much is not added.
Lift the engine cover and then remove the wing nut on the air filter cover. Remove the cover to access the top of the carburetor. Spray the liquid carb cleaner onto the carburetor and start the John Deere. Allow it to run for around 10 minutes.
Turn the mower off and replace the air filter cover and wing nut.