Few things are more frustrating than a lawn mower that refuses to turn over, no matter how hard you pull on its cord or curse its ancestry. More likely than not, your balky engine is suffering from fuel troubles—either too much, too little, or too old. Before you haul it to a shop to be fixed, try troubleshooting the problem yourself.
1. Make sure there's gas in the tank. If not, add some. (We won't tell.)
2. Give it a rest. An engine that's getting gas and not starting probably has a flooded carburetor or cylinder soaked with gasoline. Often your nose can make the diagnosis: Flooded engines reek of unburned fuel. Park the mower on level ground, and wait about 15 minutes for the gas to evaporate. Then try starting it again, with the choke off.
3. Freshen the fuel. If the engine starts and quickly stalls out, the gas may have gone bad from sitting around too long. Siphon out the tank, and add new gas. Take the old stuff to a hazardous waste recycler; dumping it anywhere else is illegal.
Tip: To reduce the chance of gas going bad, store it in a 1- or 2-gallon container so you'll have to replenish it frequently.