Gas Walk-Behind Mower: Why does my lawn mower run rough?
If your lawn mower cuts out, smokes, idles poorly, vibrates or runs erratically, it could need a good tune-up to replace the spark plug, oil and air filter. Or the problem could be with the lawn mower's fuel system. Rebuild or replace the carburetor if the engine isn't getting a good supply of fuel.
If the engine misfires, backfires, sputters or jerks the starter rope out of your hand when you try to start it, the flywheel key could be broken. A broken flywheel key disrupts the ignition timing because the magnets aren't passing the ignition coil in synchronization with piston movement. Replace the flywheel key if it's damaged or broken.
THESE REPAIRS MAY HELP SOLVE YOUR GAS WALK-BEHIND 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 won't start, runs rough or won't stay running. It's usually more effective and cost efficient to replace the carburetor rather than rebuild it.
Replace a lawn mower clogged carburetor
How to replace a lawn mower carburetor
When your lawn mower runs rough or won't start at all, the carburetor might be clogged or damaged. This DIY repair guide and video show how to replace a lawn mower carburetor in 30 minutes or less.
Rebuild a lawn mower carburetor
A clogged or dirty carburetor causes the engine to run rough or prevents the engine from starting. If you can start the engine using starter fluid but the engine won't continue to run, clogged carburetor jets may be the problem. 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.
Rebuild a lawn mower carburetor
How to rebuild a lawn mower carburetor
If your lawn mower won't start or runs rough, the carburetor could be damaged or clogged. Follow the steps in this DIY repair guide and video to rebuild a lawn mower carburetor in about half an hour.
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 or runs rough if the spark plug is bad. Replace the spark plug if it's damaged or coated with residue.
Replace a lawn mower spark plug
How to replace a lawn mower spark plug
If your lawn mower engine runs rough or is hard to start, a new spark plug could be the right fix. This repair guide and video explain how to replace a lawn mower spark plug.
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 key gets dented when the blade hits an object, the engine runs rough or vibrates severely. If the flywheel key shears when you hit an object, your lawn mower will stop running and won't start. If you inspect the flywheel key and find it dented or sheared, replace it.
Replace a lawn mower flywheel key
How to replace a lawn mower flywheel key on an OHV engine
If your lawn mower died after hitting a rock or tree stump, the flywheel key might have broken. This repair guide and video show how to replace a lawn mower flywheel key.
How to replace a lawn mower flywheel key on a flathead engine
If your lawn mower doesn't start after hitting a rock or a stump, the mower flywheel pin might have sheared to protect expensive components. This repair guide shows how to replace a lawn mower flywheel key. This guide is for older mower models that have a flathead engine.
Tune up a lawn mower
Tune up a walk-behind mower when the engine runs rough or won't start. You may need to tune up the engine when it vibrates too much or won't stay running. Regular tune-ups prevent engine wear and improve engine 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. Follow the steps in our How to tune up a lawn mower video to get your mower running smoothly again.
Tune up a lawn mower
How to replace a lawn mower spark plug
If your lawn mower engine runs rough or is hard to start, a new spark plug could be the right fix. This repair guide and video explain how to replace a lawn mower spark plug.
Symptoms for gas walk-behind mowers
Choose a symptom to see related walk-behind mower repairs.
Main causes: damaged cutting blade, loose cutting blade, damaged flywheel key, engine needs tune up…
Main causes: uneven wheel height settings, damaged wheel, dull or damaged cutting blade…
Main causes: engine needs tune up, dirty or clogged carburetor, damaged flywheel key…
Main causes: drive control cable failure, worn or broken drive belt, bad transmission, broken drive wheel…
Main causes: stale gas, engine needs tune up, bad spark plug, dead battery, bad recoil starter, faulty safety switch, ba…
Main causes: dirty carburetor, bad spark plug, clogged air filter, engine choke problems, clogged gas cap vent…
Repair guides for gas walk-behind mowers
These step-by-step repair guides will help you safely fix what’s broken on your walk-behind lawn mower.
How to rebuild a lawn mower carburetor
The carburetor mixes air with fuel to drive the piston. Rebuild the carburetor if it's clogged or leaks.…
How to replace a lawn mower recoil starter on an OHV engine
Replace the recoil starter if it doesn't move when you pull the starter rope.…
How to replace a lawn mower wheel
Learn how replace a damaged wheel on a walk-behind lawn mower—it's a quick, easy fix.…
Effective articles & videos to help repair your walk-behind mowers
Use the advice and tips in these articles and videos to get the most out of your walk-behind lawn mower.
Learn about all the convenient features on our Sears PartsDirect website that make your parts purchases easier.…
Get answers to frequently asked questions about Sears and Sears PartsDirect.…
Learn about the different kinds of mower blades and how to maintain them.…