Save yourself the headache of a clogged carburetor next spring by draining or running out the gas in your mower, tractor, weed whacker, lawn edger, and every other gas motor you can think of. It is worth the small amount of work and failing to do it is the reason why you see so many mowers and garden tools sitting out in the garbage every spring. People fail to winterize their tools, then end up throwing them away when the carburetor is gummed up.
Source: http://handyman-do-it-yourself.com