Walk-Behind Lawn Mower: Vibrates too much

If your mower has a vibration problem when the mower is running, start by checking whether the blade is damaged, imbalanced, installed incorrectly or loose. Replace it if it's damaged, following the instructions in the repair guide below. Also make sure the engine's mounting bolts are tight.

If you have a hard time pulling the starter rope and the engine sputters when starting your lawn mower, the flywheel key may be damaged.

Here's a troubleshooting video that covers a sheared flywheel key: Lawn Mower Won’t Start Troubleshooting Video: Can’t Pull Recoil Starter Rope

These repairs may help solve your Walk-Behind Lawn Mower problem:

Tune up a lawn mower

Air filter

Tune up a walk-behind mower to prevent engine wear and improve its efficiency. A walk-behind mower tune-up includes changing the oil, spark plug and air filter. It could also include sharpening or replacing the blade.

For manuals, repair guides, and specific part recommendations, enter your model number.

Replace a lawn mower blade

Blade

For safety and for a cleaner cut, replace a mower blade that's bent, chipped, broken or otherwise damaged.

For manuals, repair guides, and specific part recommendations, enter your model number.

Replace a lawn mower spark plug

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.

For manuals, repair guides, and specific part recommendations, enter your model number.

Replace a lawn mower flywheel key

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.

For manuals, repair guides, and specific part recommendations, enter your model number.