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How to Tell If a Lawn Mower Spark Plug is Bad?

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So, you decide to mow your lawn one day and discover that the thing isn’t working properly, or at all. What could go wrong? Well, there can be many things.

It could be something major like faulty wiring or something as simple as not having enough fuel for the engine to turn over. It could also be a bad spark plug; a spark plug is essential for your lawn mower to work.

First let’s look at why a spark plug is essential for your lawn mower, and how it works so that we can identify if it is truly the problem. Luckily, it’s no rocket science so anyone can pick it up.

Spark Plug — What Does it Do?

How to Tell if a Lawn Mower Spark Plug is Bad
via Pixabay

Gasoline-powered lawn mower engines are quite similar to car engines in their basic functions, they are of course much more simplified but the way they produce power is the same.

An engine needs a way to combust the air-fuel mixture to generate power. When the air-fuel mixture is ignited, it expands explosively and generates a lot of force. This is what runs your engine.

The air-fuel mixture needs a source of ignition to combust, and that is the job of the spark plug. A spark plug, as the name suggests, generates a spark between its two electrodes, causing the air-fuel mixture to ignite and powering the engine.

How Can I Tell if My Spark Plug is Bad?

Now that you understand the function of the spark plug, you can start identifying the possible issues that a faulty spark plug may cause.

Now, you might be wondering how to tell if the lawn mower spark plug is bad. As we have discussed, a spark plug’s only job is to ignite the air-fuel mixture and power the engine.

So, if your spark plug is completely dead or isn’t working properly then your engine will either not start at all or just won’t work as well.

How to tell if a Lawn Mower spark plug is bad? You will have a lot of difficulty in starting the engine, and when the engine is running, it will be running slow or weak.

Another possible sign is that the lawn mower is consuming more fuel than it used to. This can also be caused by other issues like wear and tear in the engine so it shouldn’t be your primary focus.

Fixing the Problem

What are the possible solutions to this problem? Well, you could just buy another spark plug. Lawn mower spark plugs are pretty cheap, you can get one for less than 10$.

You could also try fixing the spark plug. This, of course, only works if your spark plug is still in decent condition.

You shouldn’t waste your time trying to fix a spark plug that doesn’t work at all. If your spark plug just has a little bit of material build-up around it then you can try and fix the problem by just cleaning it.

To do this, just remove the spark plug and clean it with a soft wire brush. Don’t try to clean it too aggressively as you can cause damage to its electrodes. You can also use a spark plug spray cleaner to make the job easier.

After the cleaning is done, just install the spark plug back into your lawn mower, making sure that it fits snugly. Once the installation is done, just run the engine again and you should be good to go.

If the issues are not fixed, then you should just get a new spark plug.

How Can I Make a Spark plug Last Longer?

First of all, you should know that spark plugs are not made to last forever. They work inside the combustion chamber of an engine, so they are exposed to a very harsh environment.

The average lifespan for a lawn mower spark plug is 25 hours. This might not sound like a lot but, we don’t run our lawn mowers continuously for extended periods of time.

Now, if your spark plug does not last nearly as long as 25 hours then you can try and extend its lifespan by taking care of a few things.

Usually, if your spark plugs have a lower lifespan, it means that they are being exposed to conditions that are too extreme. Things like overheating, bad fuel, and debris can cause the spark plug to die sooner.

Luckily, you can easily fix these issues, you can avoid overheating your lawn mower engine by not running it for too long. If you have to run it for a while, then just give it a break of 5–10 minutes so it can cool down.

Bad fuel can cause an excess buildup of carbon in your engine. This excess carbon builds up on the electrodes of the spark plug and causes it to malfunction. You can avoid this by changing up the fuel in your lawn mower.

Excess debris or oil is also a common cause of material buildup on a spark plug. You can avoid this by changing the air filter of your lawn mower and making sure that there are no oil leaks in your engine.


A spark plug is essential for a lawn mower to function. The spark plug is what ignites the air-fuel mixture in the engine, this ignition causes combustion, which in turn runs the engine.

If your engine is not starting at all or just not running as well then chances are that you have a faulty spark plug.

You can easily fix this problem by either replacing the faulty spark plug or by cleaning it. Spark plugs can malfunction if they are dirty so a bit of cleaning may be needed to fix them.

Spark plugs are fairly cheap, so you should just buy a new one if things don’t improve after cleaning it. These plugs also have a limited lifespan, so, if your spark plug is at the end of its life, it should just be replaced.

To extend the lifespan of your spark plug, you should take care of a few things. Common causes of shorter spark plug lifespan are overheating debris, and carbon buildup.

These things are quite easy to take care of. Just don’t run your engine for too long, change your air filter in time and use a good quality fuel to avoid carbon buildup.