Riding Mowers & Tractors: Runs rough or misfires

If the engine runs rough or misfires, it could have a clogged carburetor. Rebuild or replace the carburetor if it's clogged. If the engine runs rough after hitting a rock or stump, check the flywheel key-a damaged flywheel key will disrupt the ignition timing.

Check for fuel, oil or carbon deposits on the spark plug. Replace the spark plug if it's fouled.

Bad fuel causes a rough-running engine. Drain the fuel tank and fill it with fresh gasoline if the fuel is over 6 months old. Use fuel stabilizer to keep the gasoline fresh.

Low cylinder compression causes a rough running engine. Check and adjust the valve lash on the engine if you find low cylinder compression.

Tune up the mower's the engine each season to keep the riding mower running smoothly.

riding mowers & tractors

These repairs may help solve your riding mowers & tractors problem

Replace the riding mower carburetor assembly

Replace the riding mower carburetor assembly

The carburetor mixes gas with air before the fuel goes into the cylinder. If the gas/air mix isn't balanced, the engine won't start or the engine will run rough and stall when you try to drive the riding mower. A damaged carburetor may also leak gas. Replace the carburetor if it causes any of these symptoms.

January 1, 2015
By Lyle Weischwill
How to replace a riding lawn mower carburetor

When a lawn tractor engine surges or is hard to start, the problem could be a clogged or damaged carburetor. This DIY repair guide and video show how you can replace the carburetor yourself.

Repair difficulty
Time required
 45 minutes or less
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Rebuild the riding mower engine carburetor

Rebuild the riding mower engine carburetor

The carburetor mixes fuel with air to create a combustible mixture that enters the engine cylinder and ignites to drive the piston. Impurities in gasoline can clog the carburetor, preventing the engine from starting. Carburetor clogs can also cause the engine to run rough and the engine may stall when you try to drive the riding mower. Seals and gaskets in the carburetor eventually wear out and can leak gas. Use a carburetor rebuild kit to refurbish a clogged or leaking carburetor.

January 1, 2015
By Lyle Weischwill
How to rebuild a riding lawn mower carburetor

Does your riding lawn mower engine run rough or misfire? The carburetor might be clogged or worn. This DIY repair guide and video show how to rebuild the carburetor in a riding lawn mower in about an hour.

Repair difficulty
Time required
 60 minutes or less
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Tune up the riding mower engine

Tune up the riding mower engine

The engine tune-up includes routine maintenance for a riding lawn mower or tractor. Engine performance suffers if you don't regularly tune up the engine. A poor-running engine may stall when you try to drive the mower. You may notice uneven cuts if the engine doesn't run smoothly when you're mowing grass. Routinely tune up the engine by replacing the engine oil, oil filter, air filter, fuel filter and spark plug. The tune-up also includes checking the ignition, carburetor, battery, throttle and choke controls, as well as cleaning the engine cooling fins.

January 1, 2015
By Lyle Weischwill
How to replace a riding lawn mower fuel filter

If your riding lawn mower’s engine runs rough or won't run, the fuel filter could be dirty. This repair guide and video show how to easily replace the fuel filter on your riding lawn mower in 15 minutes.

Repair difficulty
Time required
 15 minutes or less
Read more
January 1, 2015
By Lyle Weischwill
How to replace a riding lawn mower spark plug

If your riding lawn mower engine runs rough or is hard to start, it might be because the spark plug is damaged. This DIY repair guide and video show how to replace the spark plug on a riding mower in 15 minutes or less.

Repair difficulty
Time required
 15 minutes or less
Read more
How to replace the air filter on a riding lawn mower

If your riding lawn mower runs rough or stalls after starting, the air filter could be dirty. This DIY repair guide and video show how to replace a clogged riding mower air filter in less than 15 minutes.

Repair difficulty
Time required
 15 minutes or less
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Replace the riding mower engine fuel filter

Replace the riding mower engine fuel filter

The engine fuel filter screens impurities from the gasoline going to the carburetor. A clogged fuel filter won't allow gas to flow to the carburetor so the engine won't start. A damaged filter won't screen impurities from the gasoline, resulting in a clogged carburetor. Replace the engine fuel filter if it's damaged or clogged.

January 1, 2015
By Lyle Weischwill
How to replace a riding lawn mower fuel filter

If your riding lawn mower’s engine runs rough or won't run, the fuel filter could be dirty. This repair guide and video show how to easily replace the fuel filter on your riding lawn mower in 15 minutes.

Repair difficulty
Time required
 15 minutes or less
Read more
Replace the riding mower spark plug

Replace the riding mower spark plug

The spark plug gets electrical current from the ignition system 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. A 2-cylinder engine runs rough when one of the spark plugs goes bad. Replace the spark plug if it's damaged or coated with residue.

January 1, 2015
By Lyle Weischwill
How to replace a riding lawn mower spark plug

If your riding lawn mower engine runs rough or is hard to start, it might be because the spark plug is damaged. This DIY repair guide and video show how to replace the spark plug on a riding mower in 15 minutes or less.

Repair difficulty
Time required
 15 minutes or less
Read more
Replace the riding mower engine flywheel key

Replace the riding mower engine 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 riding mower engine stops running and won't start. If the flywheel key breaks or shears, replace it.

How to replace the flywheel key on a riding lawn mower

If the spark plug sparks but the engine won't start, the flywheel key could have sheared off (did you hit a rock and come to a sudden stop?) This repair guide and video show how to replace a flywheel key on a riding mower.

Repair difficulty
Time required
 60 minutes or less
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Symptoms common to all riding mowers & tractors

Choose a symptom to see related riding mower and lawn tractor repairs.

Main causes: dead battery, stale fuel, bad starter solenoid, ignition system problem, bad ignition interlock switch, clogged carburetor
Main causes: punctured tire or inner tube, leaky valve stem, damaged wheel rim
Main causes: damaged tie rods, bent or worn wheel spindle, worn front axle, damaged sector gear assembly
Main causes: faulty battery, bad alternator
Main causes: engine overfilled with oil, leaky head gasket or sump gasket, damaged carburetor seals, cracked fuel pump, broken fuel line
Main causes: damaged cutting blade, worn deck pulley, damaged mandrel pulley, loose fasteners on mower deck components
Main causes: worn or broken ground drive belt, bad seat switch, transaxle freewheel control engaged, transaxle failure, dirty carburetor
Main causes: shift lever needs adjustment, neutral control needs adjustment
Main causes: unlevel mower deck, dull or damaged cutting blades, worn mandrel pulleys, bent mower deck, engine needs tune up
Repair guides common to all riding mowers & tractors

These step-by-step repair guides will help you safely fix what’s broken on your riding mower or lawn tractor.

How to replace a mandrel assembly on a riding lawn mower

Replace the mandrel assembly if the blade shaft vibrates or doesn't spin.

Repair difficulty
Time required
 30 minutes or less
How to replace the air filter on a riding lawn mower

Get your mower running smoothly again by replacing the air filter—it's a quick job you can do yourself, following these steps.

Repair difficulty
Time required
 15 minutes or less
February 1, 2015
By Lyle Weischwill
How to replace a riding lawn mower ignition switch

Get your mower started again by replacing the ignition switch—it's a quick job you can do by following these steps.

Repair difficulty
Time required
 15 minutes or less
Articles and videos common to all riding mowers & tractors

Use the advice and tips in these articles and videos to get the most out of your riding mower or lawn tractor.

December 1, 2017
Wiring schematic symbols explained video
By Sears PartsDirect staff

Learn some of the most common symbols found in a wiring diagram and what they mean.

May 1, 2017
Troubleshooting a riding lawn mower blown fuse video
By Sears PartsDirect staff

Test the ignition switch and wire harnesses to find the short.

March 1, 2016
How to level a riding lawn mower deck for an even cut video
By Sears PartsDirect staff

Mower not cutting the grass evenly? Your mower deck might be the problem.