January 1, 2015

How to replace a riding lawn mower spark plug

By Lyle Weischwill
How to replace a riding lawn mower spark plug

This DIY riding mower repair guide gives step-by-step instructions for replacing the spark plug on your riding lawn mower. You'll notice the engine runs rough or is hard to start if it has a broken or fouled spark plug. To keep the mower running smoothly, replace the spark plug once a year, or as often as your owner's manual specifies. Replace the spark plug with a manufacturer-approved replacement part if it's fouled or the ceramic insulator is cracked.

Use the procedure in this repair guide and video to replace the spark plug in Craftsman, Husqvarna, Murray, MTD, Toro, Troybilt and Ariens riding mowers and tractors.

Quick links
Tools required
Spark plug wrench
Gap tool
Work gloves
Repair difficulty
Time required
15 minutes or less
Repair difficulty
Time required
15 minutes or less
Replacing a spark plug on a riding lawn mower

This video explains how to replace the spark plug on a riding lawn mower.

Instructions

  1. 01.

    Disconnect the spark plug

    Park the tractor on a level surface in a well-ventilated area and set the parking brake.

    Turn the ignition switch off and remove the key.

    Let the engine cool.

    Wear work gloves to protect your hands.

    Lift the tractor hood and disconnect the spark plug wire.

    Tip: Disconnect both spark plug wires if your tractor has 2 cylinders.
    Disconnect the spark plug.

    Disconnect the spark plug.

  2. 02.

    Remove the old spark plug

    Use a spark plug wrench to remove the spark plug from the engine.

    Tip: You can instead use a deep socket and ratchet to remove the spark plug.
    Remove the old spark plug.

    Remove the old spark plug.

  3. 03.

    Install the new spark plug

    Using a gap tool, set the gap on the spark plug to the gap specified in the owner’s manual. For this engine, the gap is .03 inches.

    Thread the new spark plug into the engine and tighten it with the spark plug wrench. Tighten the spark plug firmly, but don't overtighten, so you can remove the spark plug easily the next time you replace it.

     

    Gap the spark plug.

    Gap the spark plug.

  4. 04.

    Reconnect the spark plug

    Reconnect the spark plug wire and lower the tractor hood.

    Tip: Reconnect both spark plug wires if your engine has 2 cylinders.
Warning: Undertaking repairs to appliances can be hazardous. Use the proper tools and safety equipment noted in the guide and follow all instructions. Do not proceed until you are confident that you understand all of the steps and are capable of completing the repair. Some repairs should only be performed by a qualified technician.

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: damaged cutting blade, worn deck pulley, damaged mandrel pulley, loose fasteners on mower deck components
Main causes: shift lever needs adjustment, neutral control needs adjustment
Main causes: engine overfilled with oil, leaky head gasket or sump gasket, damaged carburetor seals, cracked fuel pump, broken fuel line
Main causes: punctured tire or inner tube, leaky valve stem, damaged wheel rim
Main causes: worn or broken ground drive belt, bad seat switch, transaxle freewheel control engaged, transaxle failure, dirty carburetor
Main causes: unlevel mower deck, dull or damaged cutting blades, worn mandrel pulleys, bent mower deck, engine needs tune up
Main causes: worn or broken blade belt, broken belt idler pulley, blade clutch cable failure, bad PTO switch, damaged mandrel pulleys
Main causes: clogged carburetor, damaged flywheel key, dirty spark plug, stale fuel, improper valve lash, engine needs a 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 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
How to replace the starter motor on a riding lawn mower

If you hear the solenoid click but don’t hear the starter motor spin when you turn the key, follow these steps to replace it.

Repair difficulty
Time required
 30 minutes or less
January 1, 2015
By Lyle Weischwill
How to replace a riding lawn mower blade

If a blade on your mower is dull or bent, replace it following the steps in this repair guide.

Repair difficulty
Time required
 30 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.

May 1, 2017

Riding lawn mower engine spins but won't start video

By Sears PartsDirect staff

Troubleshoot fuel, spark and compression issues.

May 1, 2017

How to repair a riding lawn mower tire video

By Sears PartsDirect staff

Learn when you can use sealant to fix a flat tire.

June 1, 2016

How to mow a lawn for healthier grass

By Erin Hynes

How often and tall you mow your lawn has a big impact on its health. Check out these 3 rules.