Walk-Behind Lawn Mower: Doesn't start well
If your lawn mower has trouble starting, or it doesn't start at all, make sure the tank has fuel and that the fuel is fresh; stale fuel can become watery and won't ignite well. Another cause could be a clogged carburetor or a problem with the ignition system.
Check out the list of repairs below and watch our troubleshooting videos for more possibilities.
These repairs may help solve your Walk-Behind Lawn Mower problem:
Replace a lawn mower clogged carburetor
A clogged orifice or jet in a carburetor prevents the engine from getting the mix of gas and air it needs. When the carburetor is clogged, the engine sputters and dies when you try to start it. It's usually more effective and cost efficient to replace the carburetor rather than rebuild it.
Rebuild a lawn mower carburetor
A clogged or dirty carburetor causes the engine to run rough or prevents the engine from starting. Clean and rebuild the carburetor using a carburetor rebuild kit if the engine won't start or it runs rough because the carburetor isn't supplying the engine with fuel.
Tune up a lawn mower
Replace a lawn mower ignition coil
The ignition coil sits next to the flywheel and generates electrical current to fire the spark plug when magnets on the flywheel pass the ignition coil. If the ignition coil fails, the engine won't start because the spark plug doesn't fire. Connect a spark plug tester to the engine to see if the spark plug is getting electrical current from the ignition coil. If the ignition coil doesn't work, replace it.
Replace a lawn mower spark plug
The spark plug gets electrical current from the ignition coils and sparks to ignite the fuel mixture in the cylinder, which drives the piston. The spark plug won't spark if it's coated with carbon deposits or oil residue, or if there’s a crack in the ceramic insulator. The engine won't start if the spark plug is bad. Replace the spark plug if it's damaged or coated with residue.
Replace a lawn mower flywheel key
The flywheel key is a small metal rectangle that keeps the crankshaft and flywheel aligned when you tighten the flywheel nut. To protect more expensive components from damage, the flywheel key is designed to shear if the mower blade hits an object like a rock or tree stump hard enough to make the flywheel slip out of alignment with the crankshaft. If the flywheel shear slightly, the engine runs rough or misfires. If the flywheel key breaks or shears severely, your lawn mower stops running and won’t start. If the flywheel key breaks or shears, replace it.
Replace a lawn mower recoil starter assembly
The recoil starter on top of the engine has a spring that retracts the starter rope used to pull-start a gas mower. If the rope doesn't retract after you pull it, it's likely the spring is broken. Replacing the spring itself is difficult and dangerous, so the best way to repair a recoil starter is to replace the whole recoil starter assembly.
Replace a lawn mower safety switch
The engine safety switch on a walk-behind lawn mower stops the ignition coil from sparking and has a brake pad that slows the flywheel. If the safety switch fails, the engine might not turn off (in that case, remove the spark plug wire to kill the engine). A failed switch prevents the ignition coil from sparking the spark plug. If the coil isn't sparking, remove the kill wire from the ignition coil and check the engine for spark. If there's spark, replace the safety switch.
Charge or replace a lawn mower battery
If the electric start on your walk-behind lawn mower doesn't work, it might not be receiving power from the battery. Batteries fail over time or if improperly maintained. If charging the battery overnight doesn't correct the problem, replace the battery.