Bad Lawn Mower Spark Plug – Signs + How to Change It

With time, a lawn mower spark plug gets dirty or worn out. In this state, it will no longer produce a powerful spark required for ignition and running of the engine. If you are having trouble starting your lawn mower, experiencing less power when mowing or using more fuel, then you need to clean or change the mower’s spark plug.

A spark plug is a small cylindrical device fitted on the engine to deliver an electrical spark that ignites gasoline/air mixture in the combustion chamber, allowing the engine to start and continue running. Like other parts of the engine spark plugs can fail and affect your mowing schedule.

A number of things can make a lawn mower spark plug to go bad. They include age, moisture, overheating, damage to the electrodes, carbon buildup and oil deposits on the spark plug. Any of these issues can make your spark plug to become less effective or completely fail in its performance.

What do bad spark plugs look like?

Although various signs can tell you that your lawn mower has bad spark plugs, physical inspection can give a clear picture of how things are. If your lawn mower won’t start after sitting or you tug repeatedly on the wind to start the engine then spark plugs are a culprit and you need to physically inspect them.

Start by disconnecting the spark plug wire from the engine. Use a wrench and a recommended spark plug socket to remove the spark plug from the engine. Then carefully examine both ends of the spark plug and the socket where it sits. If the spark plug is bad it will appear as follows:

  • Black with chunk of carbon buildup in the gap between the sparking end and the hook-shaped piece of metal on the spark plug end.
  • Simply dark with carbon residue built up on the ends but not spanning the gap
  • Gas or oil residue on the spark plugs and/or where they sit
  • Physically damaged on the end with the overhanging piece of metal

Sometimes it can be impossible to tell if a spark plug is bad or damaged by just using your eyes. The component can fail internally causing its electrical system to stop working. It is also a problem when the sparking gap has increased to exceed the required size. This will need an expert to check and fix.

Depending with the kind of issue affecting your spark plug, you’ll need to clean or replace it for everything to resume operation. This should be done in line with manufacturer’s recommendations in the owner’s manual.

How to Change Lawn Mower Spark Plug

Changing a lawn mower spark plug is a simple DIY task that involve locating where the spark plug is, removing it using a spark plug socket and replacing with a new one designed for your lawn mower model. You may also clean the dirty spark plug and reuse it. Here are the steps:

  1. Purchase the right type of spark plug for your lawn mower as directed in the user manual. Spark plugs are not universal.
  2. Position your lawn mower on a flat ground and ensure you can locate where the spark plug is on engine. Sometimes it may be covered in the mower housing.
  3. Disconnect the spark plug cable to prevent the engine from accidentally starting
  4. Fit the spark plug socket over the plug and turn counterclockwise to remove it. If it’s too tight, apply a WD-40 or any lubricant and wait for it to soften for easier removal.
  5. Install the new spark plug and gently tighten it using a spark plug socket and wrench where necessary. Be careful not to overtighten it as this can damage it.
  6. Now reconnect the spark plug wire and start the lawn mower engine for testing.

Pro Tip: Spark plugs should be changed every season during a lawn mower tune up. This should be in spring as you prepare to start mowing. Spark plug inspection should be done after every 25 hours of use or more often when owing in harsh conditions.

How to clean lawn mower spark plug

Sometimes after inspection, you may realize that your mower’s spark plug can be cleaned and be used again. This is especially when you recently installed it and you can see a carbon buildup or oil deposits around it during the inspection. Here is how to clean a spark plug:

After removing it from the engine, use a recommended spray-on cleaner and a wire brush to remove any buildup. Before reinstalling it, ensure the component is in good condition without burned electrodes or cracked ceramic.

You will also have to measure the gap between the curved and straight electrodes using the spark plug gauge. Few adjustments may be needed to correct any increase in the size of the space. This is simply done by gently bending the curved electrode inwards using a gauge.

Final Though

Bad lawn mower spark plugs can give you a bad mowing experience when the season comes. Regular inspection, cleaning and changing the plug is necessary for the health of a lawn mower. Without doing this, you will have problem starting your lawn mower, using more fuel and engine breakdowns during mowing.

Leave a Comment

Your email address will not be published.