When you can't start your mower, make sure the tank has fuel and that the fuel is fresh; stale fuel can become watery and won't ignite well. Tune up the mower's engine to give it the best chance of starting. Check the spark plug and replace it if it's covered with oil or other deposits.
If your mower uses a battery, charge or replace the battery if it won't power the starter to spin the engine. If you have to pull the starter rope to start the engine, replace the recoil starter if it doesn't spin the engine when you pull the rope. Replace the starter rope if it's broken. For additional help, watch our can't pull the recoil starter rope and how to fix a pull cord stuck after tipping mower videos.
Replace the safety switch or the ignition coil if the spark plug isn't getting current through the ignition system. The engine won't start if you hit a rock or stump and shear off the flywheel key, so replace the flywheel key if it's broken. Our spark plug and ignition problems video provides additional troubleshooting tips when the engine isn't getting any spark.
Carburetor problems often prevent a mower engine from starting. Replace or rebuild the carburetor if it's clogged. Our fuel, ignition and compression video has more help troubleshooting fuel problems.