How to Change Your Lawn Mower Spark Plug

Gloved hands changing a lawnmower spark plug

When your lawn mower has trouble starting, one of the first things to check is your spark plug. Your spark plug, as the name would suggest, generates the spark that initiates fuel combustion and gets your mower running. If it is dirty beyond cleaning or damaged enough to make starting difficult or impossible, replacing it is your best option.

NOTE: Before removing your old spark plug and replacing it with a new one, consult your lawn mower’s operating manual for all pertinent safety information.

Replacing your lawn mower’s spark plug is a straightforward process, so we’ll break it down into steps for removing your old plug and then steps for installing the new one.

Removing Your Old Spark Plug

  1. Disconnect the spark plug lead. Check the wire for any signs of damage and ensure that the connector is clean.
  2. Carefully examine and clean the area around the plug to keep debris of any kind out of the combustion chamber.
  3. Remove the old spark plug with a spark plug or socket wrench in accordance with the instructions in your owner’s manual.

Take the time to examine your old spark plug before installing a new one. Search for obvious signs of degradation, damage, or accumulated deposits near the tip or on the shell. If you see any of these signs, continue to the instructions for installing the new plug. If you don’t, consider taking your lawn mower into your local service dealer to make sure the spark plug is really the issue. There are few things more frustrating than replacing a spark plug and then finding out it’s another problem keeping your mower from running.

Installing the New Spark Plug

The best way to get a replacement spark plug is to bring your lawn mower’s model and serial number to your local service center. They will make sure you get the correct plug for your machine and can answer any questions that you may still have.

  1. Double-check the spark plug gap matches your machine’s specs with a gap tool.
  2. Hand-screw the new spark plug four or five turns. It should be finger-tight at this point.
    • If you can’t turn it this many times by hand, bring your lawn mower to your authorized dealer to keep from damaging your engine.
  3. Use your wrench to slightly tighten the plug based on the specifications in your operating manual.
    • Beware! Tightening the spark plug too much can damage your lawn mower’s engine.
  4. Reattach the spark plug lead with the connector vertically positioned and securely fastened to the end of the spark plug.

Lawn Mower Spark Plug Replacement Video

Check out our helpful video for a visual guide for changing your lawn mower’s spark plug. For a full transcript, see the end of this article.

Replacing spark plugs often?

If you notice your lawn mower spark plug fouling or wearing quickly, it could be some of these common issues:

  • An incorrect plug
  • Excessive idling
  • Too rich a fuel mixture
  • Low engine compression

If you need help with these or any other causes of quickly failing spark plugs, see your local Toro service dealership.

Back to Mowing!

After you have replaced your mower’s spark plug, it’s time to start it up and make sure everything is operating as it should. You should notice smooth idling and acceleration, especially in comparison to what you were experiencing with your old plug. Expect to see some fuel efficiency gains as well. Once you’re back up and running, you’re well on your way to a summer of easy starts and high-quality performance out of your lawn mower!

Video Transcript

The following is the transcript for our video above:

Having trouble starting your lawn mower? The problem might be your spark plug.

You probably know that this little plug produces the powerful spark that starts your mower. If it gets fouled or starts to fail for some other reason, your engine will be harder to start. Before you replace your spark plug, be sure to read the important safety information in your operator’s manual. Then just follow these simple steps.

  1. Disconnect your spark plug lead and give it a quick once-over to make sure the wire is in good shape and the connector is clean.
  2. Clean the area around the spark plug to keep any dirt or debris out of the combustion chamber.
  3. Then, remove the spark plug with a socket wrench or spark plug wrench. Your local Toro service dealer is the best place to get the correct replacement spark plug for your machine. Bring your machine’s model and serial number so you’re sure to get the right plug.
  4. Today’s spark plugs come pre-gapped, but it’s a good idea to double-check this before installation.
  5. Use a gap tool and make sure the gap matches the specs for your machine.
  6. Screw the new spark plug in by hand for 4 to 5 turns. If you aren’t able to do this – stop and bring the machine to an authorized Toro service dealer. We want to avoid cross-threading the plug, which would damage your engine.
  7. Once the plug is finger tight, use your wrench to tighten the plug that’s specified in your operator’s manual. This should be a very minor adjustment.
  8. Do not over-tighten, as that can cause damage to your engine.
  9. Finally, reattach the spark plug lead and make sure the connector is positioned vertically and seated securely on the end of the plug.

And that should be all it takes to restore a healthy ignition spark. Now just start it up and go!

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