How to Replace a Lawn Mower Spark Plug? (step-by-step process you need to know) – Gardener Corner

How to Replace a Lawn Mower Spark Plug? (step-by-step process you need to know)

Needless to say, spark plug electrodes should be sharp and clean. Only then do they produce powerful sparks to activate the ignition. So it’s only natural for dirty or worn-out spark plugs to increase the tug effort on rewind. In simple words, this means more effort for producing adequate sparks. Maybe it’s time you learn how to replace a lawn mower spark plug.

Lucky for you, spark plugs are the most affordable and easiest engine parts to replace.

How to Tell If a Lawn Mower Spark Plug Is Bad

You can determine the current condition of the spark plug of your lawnmower using the following steps.

  1. First off, disconnect the wire of the spark plug.
  2. Then remove the plug.
  3. Now it’s time to inspect the spark plug electrode. What you’re looking for are any visible signs of damage.
  4. Check the electrode condition as well. Is it normal, gas-fouled, carbon-fouled, or wet?
  5. If that electrode looks damaged or worn out, it’s time for a replacement.

The best way to go about it is to check the engine. Is it more difficult to start? The engine starts as a result of two very important principles. The first is gas and the other is the spark. The chances are you’ve just loaded up the gas tank. So it’s more likely that the problem is due to the absence of spark.

The engine of push mowers tends to stutter. So it may take a few cord pulls to start. In some cases, engines of sit-on type tractor mowers don’t start on the very first turn of its key. At the time of running, that engine is also quite susceptible to cutting out. This means you have to go through the trouble of restarting the engine of your lawnmower once again.

Slower acceleration and lack of power are also two very likely possibilities. They start off as subtle issues. But eventually, become more apparent. So don’t neglect such warning signs that point in the direction of a bad spark plug.

Other Signs of a Damaged or Worn-Out Lawnmower Spark Plug

Flooded Engine

When the engine of your lawnmower is running, the thing can unexpectedly cut out for no apparent reason. Now you might already know what a spark plug does. So it’s easier for you to understand what’s going on and why.

The most common reason for engine cut-out is a weak spark created by the spark plug. When the spark is weak, you simply cannot expect proper fuel ignition. And when the fuel doesn’t ignite, it fails to mix with air present inside the carburetor. The outcome of which is a flooded engine. It’s because more fuel is entering the cylinder and not being subjected to effective burning.

Increased Gap Between Firing Electrodes and Spark Plug Center

Let’s assume that the engine of your lawnmower runs for a longer time. So it’s not uncommon for the spark plug to become hot. And when that occurs, the gap present between the firing electrodes and spark plug increases. This, in turn, weakens the ignition spark further.

So it’s important to allow your lawnmower to rest. And to cool down once the engine starts cutting off. Don’t keep trying to start the thing repeatedly. Give it a break.

Too Much Gas Consumption

Another common warning sign takes the form of excessive consumption of fuel. Do you find yourself filling the engine more frequently with gasoline? If yes, then the cause might be damaged spark plugs.

The thing about gas not burning off completely or inefficiently is that it increases fuel consumption. This is where fuel efficiency takes a nosedive.

Since the gasoline is failing to burn out, you can also expect some fuel smell around the mower. The smell is the same as raw gasoline.

How to Replace a Lawn Mower Spark Plug

It’s a very straightforward process; the task of replacing the spark plug of your lawnmower. To be honest, it’s the easiest of all the maintenance tasks. You only require a gauge, socket for the spark plug, and ratcheting socket driver.

Before you begin, ensure that the engine of your machine is cool. Don’t even attempt to perform the replacement process if the engine is hot.

And do you know the location of the spark plug on your lawnmower? For beginners or first-timers, it’s installed below the black-colored wire of the spark plug. Just disconnect the wire to inspect the plug.

  • The very first step is to make sure the replacement spark plug and damaged one is of the same shape, size, and model. Just look at the mentioned reference numbers. You’ll find them on the white-colored insulator.
  • Now disconnect the lead of the spark plug. Then clean the space around it.
  • With the help of a socket driver, remove the worn-out spark plug. You can even use a wrench for the same. It’s possible that the task might not be easy. But you can make it so by adding a little bit of lubricant and letting it soak for around 10 minutes.
  • After removing the old part, check the electrode for determining the performance of the engine. When the electrode is wet, the problem may be due to the choke system of the engine. And if it’s powdery or too dry, the issue lies with the mounting gasket of the carburetor. Or the thing could be oil-starved!
  • And the last step requires you to insert the brand new lawnmower spark plug into the engine hole. Always turn the plug using your hand until it stops turning. This ensures the prevention of cross-threading the spark plug.

After that, it’s okay to make use of the wrench. You can use a socket driver or wrench for tightening the plug. Just don’t over-tighten. Keep the fit a bit snug. Then connect the wire of the spark plug securely.


If you want your spark plug to function properly, then you’ve got to know how it works and what it does. Even how to replace a lawnmower spark plug is useful knowledge.

The component is a small electrical gadget that fits into the cylinder head of the engine. It sparks fuel ignition for creating combustion within the engine. So when damaged or worn-out, it can give rise to all kinds of problems.


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