March 1, 2016

How to replace a lawn mower spark plug

By Lyle Weischwill
How to replace a lawn mower spark plug

This lawn mower repair guide shows how to install a new spark plug on a lawn mower. The spark plug ignites the air and fuel mixture in the engine to start the lawn mower. If the engine runs rough or is hard to start, check the spark plug and replace it with the manufacturer-approved replacement part if the enamel body is cracked or the electrode is fouled with carbon or other buildup. Manufacturers recommend changing the spark plug when you tune up your lawn mower each year.

Use this procedure to replace the spark plug in Craftsman, Husqvarna, MTD, Murray, Poulan, Toro, Troybilt, Snapper and Weed Eater walk-behind lawn mowers.

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

This video explains how to replace a spark plug on a walk-behind lawn mower.

Instructions

  1. 01.

    Disconnect spark plug wire

    When the engine is cool, disconnect the spark plug wire from the spark plug. 

    Disconnect the spark plug.

    Disconnect the spark plug.

  2. 01.

    Remove the spark plug

    Use a spark plug wrench to loosen and remove the spark plug.

    Remove the spark plug.

    Remove the spark plug.

  3. 03.

    Gap the new spark plug

    Use a spark plug gap tool to set the gap between the center electrode and the ground electrode. The gap specifications for your model are in the owners manual.

    Gap the new spark plug.

    Gap the new spark plug.

  4. 04.

    Install the new plug

    Thread the spark plug into the engine. Then tighten the spark plug with a spark plug wrench. 

    Install the new spark plug.

    Install the new spark plug.

  5. 05.

    Reconnect spark plug wire

    Reconnect the spark plug wire and start the mower to make sure it runs. 

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 for gas walk-behind mowers

Choose a symptom to see related walk-behind mower repairs.

Main causes: drive control cable failure, worn or broken drive belt, bad transmission, broken drive wheel
Main causes: uneven wheel height settings, damaged wheel, dull or damaged cutting blade
Main causes: stale gas, engine needs tune up, bad spark plug, dead battery, bad recoil starter, faulty safety switch, bad ignition coil
Main causes: dirty carburetor, bad spark plug, clogged air filter, engine choke problems, clogged gas cap vent
Main causes: damaged cutting blade, loose cutting blade, damaged flywheel key, engine needs tune up
Main causes: engine needs tune up, dirty or clogged carburetor, damaged flywheel key

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.

March 1, 2016
By Lyle Weischwill
How to replace a lawn mower drive cable

The drive cable engages the transmission to spin the drive wheels and move the mower across the grass. Replace the drive cable if it's broken or frozen up inside the sheath.

Repair difficulty
Time required
 60 minutes or less
April 1, 2013
By Lyle Weischwill
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.

Repair difficulty
Time required
 15 minutes or less
April 1, 2013
By Lyle Weischwill
How to replace a lawn mower safety switch

The safety switch stops the engine when you release the lever on the handle. This repair guide explains how to replace it if it's not working correctly.

Repair difficulty
Time required
 30 minutes or less

Articles and videos common to all walk-behind mowers

Use the advice and tips in these articles and videos to get the most out of your walk-behind lawn mower.

October 1, 2019

Types of walk-behind mower blades video

By Sears PartsDirect staff

Learn about the different kinds of mower blades and how to maintain them.