How to Change a Spark Plug in a Lawn Mower?

Your lawn mower, like any machine, desires regular care and maintenance to let you enjoy its peak performance. Tending to your mower engine when required keeps the engine running, which in the long run saves you money on expensive purchases and repairs.

The spark plug is an important part of your lawn mower. It is an ignition source for the engine that powers the lawn mower. But a foul, dirty, and old spark plug is a hindrance that fails to create the spark, not allowing the engine to run.

If there seems to be a problem in starting the lawn mower engine, then the problem could lie in the spark plug, which means that you should change the lawn mower spark plug without delay.

Spark Plug For Lawn Mower

A spark plug

The spark plug is not a complicated device. It is made of a center electrode that is encased in a porcelain sheath to offer protection, a firing electrode, and a threaded shank that helps in its installation on the engine block.

Mowing gets difficult when the lawn mower spark plug gets damaged. Here are a few signs to watch out for, which is a clear signal that your spark plug needs a change.

  • It becomes difficult to start the lawn mower with the bad starter. This is because the spark plug could be weak to ignite the air and fuel mixture which the carburetor has delivered to the cylinder already.
  • The engine starts but dies out immediately. 
  • A damaged spark plug also causes misfires and popping.
  • If you feel the need to refill the gasoline tank more often than you normally used to do then the spark plug could be the sole culprit. A bad spark plug causes the gasoline to burn inefficiently or incompletely.
  • The physical appearance of the spark plug can give further clues on if or not you should change it.

Learning the proper ways to check and clean the spark plug is crucial if you own a lawn mower. And luckily for you, spark plugs are also one of the simplest components in the engine, easy and inexpensive to repair or replace.

This article lays out the steps to help you change a spark plug in a lawn mower all by yourself without any professional help. It is a straightforward process that can be undertaken even by a beginner with total confidence.

Change Lawn Mower Spark Plug: Steps to Follow

Here we lay down the detailed DIY steps, handholding you through the entire process of changing the spark plug in your lawn mower.

Step 1: Look for signs that your spark plug needs changing

Spark Plug must change now

Spark plugs are not meant to last through the entire life of the mower. They wear out fast and, in turn, impact how your engine runs. Maintain a calendar to change the spark plug to ensure that the engine does not turn inefficient.

There could be times when you may have to change the spark plug earlier in case of damage. If you notice any of the points mentioned above, namely a drop in fuel efficiency, difficulty in starting the mower, or the engine stopping suddenly, then rush to see if the problem lies in the spark plug.

Step 2: Research and buy the right kind of spark plug

right kind of spark plug

Spark plugs do not come in a standard size. You thus need to ensure that you buy one that is meant for your mower. The best would be to check the owners’ manual to determine the right match for your mower.

The spark plug has a ceramic insulator that has the number printed on top of it. You also should cross-check to see if the replacement is acceptable with the engine’s model and make.

Step 3: Correctly position the lawn mower

Before you start to work, set the mower on a stable and flat surface. This will give you complete access to the engine without compromising on safety.

Here are the tools that you would need

  • Screwdriver
  • Spark plug socket
  • New spark plug
  • Drive socket wrench in measurements of 1/2 inches or 3/8 inches as per what your machine needs
  • Wire brush
  • Feeler gauge
  • Spray-on cleaner
  • Sturdy knife

The engine should be cool before you begin the work. Let it stand for half an hour else, and you may burn yourself when you touch the mowers’ hot metal pieces.

Step 4: Disconnect the spark plug lead 

Disconnecting the spark plug lead

You will need a screwdriver to remove the engine if it is covered. Disconnect the ignition cable or the spark plug lead. This wire links the plug, the source of voltage, and the distributor, which feeds the mower with electricity. The connection should be severed so that it is safe.

Take time to check the cable. With time and excessive use, the cable could wear off, which hampers the performance of the mower. The easy to notice signs are wires with damaged jackets. If you see some broken plastic pieces, then this signals a replacement.

Step 5: Take out the spark plug

The spark plug socket should be fit on the plug and turned in a counter-clockwise direction to loosen it. Do not force if you find it difficult to ratchet it since this could cause further damage. Instead, you can apply some lubricant and let the plug soak for some time, after which you can easily take out the plug.

You should use a spark plug socket since they function to protect the ceramic insulator. It is always recommended to use the right tools to remove or install the spark plug; otherwise, this can cause damage.

Step 6: Inspect and clean the plug

Most likely, you will find the plug coated with build-up. Use a spray-on cleaner and a wire brush to clean the spark plug. If there are any stubborn deposits, then you will need a knife to scrape and chip them.

Next, have a look at the component. Suppose the part looks like it is in good condition and there is still some life left, then put it back. However, if there are any burnt electrodes or if you notice a cracked ceramic, then this signals a replacement.

Step 7: Use a spark plug gauge to adjust the gap

 spark plug gauge to adjust the gap

Take care to check the gap in the plug before you start the installation. Measure the gap between the straight and the curved electrode with the spark plug gauge. If the size is right for your mower make and model, then you will need only some basic adjustments. If you have to adjust the gap, then bend the curved electrode using the gauge.

Step 8: Install the new spark plug

It is now time to install the new spark plug. Put it in its place and turn it in the clockwise direction. Once the thread catches, use the socket to tighten it further. Take care not to overtighten it lest it may break the delicate parts.

Ratchet till the plug starts to go down and then give it a final quarter turn. This will safely install the spark plug in its right position.

Step 9: Reconnect the lead

Once the spark plug is in its place, you need to reconnect the lead. You may even want to check and replace the cable. To install the lead, replace the hood of the mower and tighten the screw.

Step 10: Disposing the damaged part

Congratulations! You have successfully changed the spark plug. If it is a full replacement, then you will have to dispose of the old parts. You can safely throw the plugin in the garbage. For the other auto scraps, make some money by selling them in the scrap yard.


We hope to have guided you well on the detailed steps of how to change the lawn mower spark plug. Make it a habit to check the components at least once in a season, with every 25 hours of mower usage or if your lawn mower does not start. You must carry out regular maintenance to let your equipment run smoothly. Else you have to either repair or replace your lawn mower.

With the confidence to change the lawn mower spark plug yourself, you can look forward to a high-performance mower, a beautifully laid lawn, and more cash in your purse.

About Jennifer Igra

Growing up in Brooklyn, New York City known for it’s green gardens. Jennifer, a 30 year old gardener and green living fanatic started Igra World to share her gardening journey and increase gardening awareness among masses. Follow Igra World to improve your gardening skills.

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