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.

Repair difficulty:
Time required:

Less than 15 min.

Parts Required

  • Spark plug

Tools Required

  • Spark plug wrench
  • Spark plug gap tool

Before you begin

Let the engine cool. 

Wear gloves to protect your hands. 


 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.

How to Replace the Spark Plug on Your Lawn Mower

Step 1: Disconnect spark plug wire

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

Step 2: Remove the spark plug

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

Step 3: 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.

Step 4: Install the new plug

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

Step 5: Reconnect spark plug wire

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