well since i work at a mower repair shop, let me say that 70% of the equipment that comes in for repair is due to leaving fuel in the equipment. like others have said, drain the fuel out of the tank, and then run the equipment dry. but lets take it a step further. buy a quality gas stabilizer,mix that with you can of gas according to instructions, (do not mix in equipment gas tank!) drain any gas without stabilzer out of equipment, then add small amount of new gas with stabilzer, and run dry. ive had great succes with fuel stabilizers. briggs & stratton makes a fuel stablizer that lasts for up to 24 months. even though you have essentially got all of the fuel out by running the equipment "dry", theres always a small amount left, and even that small amount can gum up the main jets in the carb. by adding the fuel stabilzer, its extra insurance that you wont have any other problems come next time you need to use your equipment.
wes