How to tell if a lawn mower spark plug is bad is not that difficult a question to answer as there are clear signs you can observe – your lawn mower not being able to start, having a hard time in pulling the cord, and the lawn mower’s performance being below standard.

How to Tell if a Lawn Mower Spark Plug is Bad

In this article, you can learn how to check if your spark plug is bad and how to clean and replace it if needed.

Thus, you can change your lawn mower spark plug without any hesitation. Continue reading to gain new knowledge this article can bring to you about how to best maintain your lawn mower’s spark plug and fix your mower yourself.

How To Find Out if Your Lawn Mower Spark Plug Is Bad?

To find out if your lawn mower spark plug is bad, you should look out for signs like your mower not starting at all or struggling to start, having a hard time pulling the cord, the lawn mower showing bad performance, the physical appearance of the spark plug, etc.

– Whatever You Do, Your Lawn Mower Never Starts

If, after many tries you do not get your lawn mower to start up and you have checked for other issues, it could quite possibly be the spark plug. It is specifically telling if you do not see any lawn mower spark from the combustion chamber after trying to pull the cord for ignition several times. This is a quick sign of a bad spark plug.

– Having a Hard Time Pulling the Cord of the Lawn Mower To Start

Having to exert extra effort when pulling the cord repeatedly to start the engine is another sign that the spark plug is in a bad condition.

Reasons Lawn Mower Spark Plug is Bad

One pull on the cord should be enough to initiate a spark and start the engine, but after pulling the cord many times and still no ignition takes place, stop and check your spark plug; it might be bad. 

– Lawn Mower Shows Bad Performance

As having used your lawn mower for some time, you already know its capability and capacity when it comes to its function of cutting the grass. If you notice something unusual like having a hard time cutting the grass and if you hear any changes in the sounds coming from the mower, the lawn mower spark plug needs to be checked immediately. 

– Lawn Mower Needs to be Refueled More Than it Used To Do

Experiencing an “on and off” situation with your lawn mower again and again while in use can lead to excessive fuel consumption. You also have to remember that unusual fuel consumption like refueling more than the way you used to do is also a sign of a bad spark plug.

This is because when a spark plug does work correctly the gas does not burn efficiently or completely. Because the fuel will not be properly burned up you can also expect a smell of gas when the mower is in operation.

– Lawn Mower’s Spark Plug Has an Increased Gap

Aside from the signs and symptoms already mentioned, a spark plug gap also indicates a faulty spark plug. The spark plug gap is the distance between the two electrodes. The spark plug gap can occur when the lawn mower’s engine becomes hot because of long hours of use. The hotness coming from the engine increases the gap. 

Meanwhile, the gap decreases when the engine turns cold. So, given this situation, it is advisable to always cool down the engine first before starting it again.

– Its Physical Appearance

If you suspect the spark plug you should remove it and examine its appearance in detail. For a start, if the center electrode has a rounded top, there is a problem. It should be flat. Also look for cracks or chips in the porcelain casing or pitting on the firing electrode.

How To Remove a Spark Plug That Is in Bad Condition?

To remove a spark plug that is in bad condition, you should remove the spark plug lead, prepare a spark plug socket, determine the damage and clean or replace the spark plug and then, finally, reconnect the spark plug.

All you need is a little bit of knowledge and patience!

– Remove the Spark Plug Lead

Slowly and gently pull the rubber cap from the spark plug. This procedure may require you to start wiggling the rubber cap from the plug back and forth for it to be removed successfully .

– Prepare a Spark Plug Socket

To remove the plug, you will be needing a spark plug socket. This is a type of socket that is designed to remove the mower’s spark plug without causing any damage and harm. Carefully slide the socket over the spark plug, and then gently turn it until the plug can be safely and freely removed.

– Once You Remove the Plug, Determine the Damage

After you successfully remove the plug, you can proceed to look for any damage and find out if you have one bad mower spark plug. The plug can contain damages that look like build-ups of black carbon on the electrodes.

– Clean or Replace the Spark Plug

Using a soft wire brush is recommended if you are cleaning carbon build-ups on the spark plug’s surface. If oil is present on the plug, this indicates a problem within the engine. The seals of the engine most likely degraded enough for the oil to enter where the plug is located. This is, of course, a whole other issue and should be dealt with as such.

Solutions Lawn Mower Spark Plug is Bad

If you prefer, replacing the spark plug is fine. It is usually cheap and easy to find at home and other repair supply stores. By regularly replacing the spark plug, you will be able to take good care of your lawn mower and extend its lifetime.

– Reconnect the Spark Plug

Whether you are going to replace the spark plug or clean it, you always need to return the spark plug the same way you unplug it. Any kind of dirt or fallen debris should not be able to enter the area to which the plug will be attached. Gently take the plug, and then carefully thread it into its engine the exact same way you detached it. Spark plugs should not be attached really tight, so always be careful – the recommended attachment is 15 ft. lbs.

Remember that any brand of lawn mower spark plug has a size that falls into the common standard measure. Spark plugs for lawn mowers chart for both push mower spark plugs and riding mower spark plugs shows a similar range in terms of diameter, pitch, and reach.

If you have followed all the steps, tried everything you know, and still nothing happened to resolve your issues with your mower spark plugs, it is time to think of another action plan. Call a professional or get a tune-up kit online.

They are complete with an oil filter, air filter, spark plugs, fluid fuel stabilizer, lawn mower oil, and others. All that will surely suit the needs specific to your mower engine.

– Take Care of Your Lawn Mower’s Spark Plug

To take care of your lawn mower’s spark plug, you can ensure the spacing is correct, clean them on a regular basis using the correct methods, and install them correctly. However, no matter how well you look after them, they will fail at some stage and need to be replaced.

How long does a lawn mower spark plug last will depend on how you maintain it. Lawn mower spark plugs usually last for about 25 hours. The lawn mower and its parts and engine need to be checked regularly according to the user’s manual as they all influence each other.

Frequently Asked Questions

When Is the Perfect Time to Clean Your Lawn Mower Spark Plug?

The perfect time to clean your lawn mower spark plug is before it gets so dirty that it stops working! When something is wrong with your spark plug, you need to assess it properly to determine whether you need to do some cleaning or replace it for a new one. 

What Equipment Do You Need to Clean Your Spark Plug?

The equipment you need to clean your spark plug is easy to find and cheap to buy: pliers, wrench and spark plug socket, plastic brush and soft wire, brake cleaner or rubbing alcohol, paper towels or rags, and a spark plug gap tool.

How Do You Test a Lawn Mower Spark Plug With a Multimeter?

To test a lawn mower spark plug with a multimeter, follow these steps:

  • The engine should be dry.
  • Detach the spark plug from the engine.
  • The multimeter should be set to a 20k Ohm range.
  • Position the probes at the ends.
  • Check the spark using the multimeter.


You can now tell if a lawn mower spark plug is in bad condition by simply remembering all the signs and symptoms that may indicate that your spark plug is in a bad condition, as stated in this article. Let’s recap every detail we mentioned in this article to make sure that you are ready to tell whether a lawn mower spark plug is bad.

  • You can now determine whether a lawn mower spark plug is for cleaning or replacement depending on its condition.
  • If your lawn mower spark plug is in a bad condition, follow the steps provided in this article to assess and resolve.
  • Give your lawn mower some time to rest and cool down before using it again.
  • Just like any other tool or equipment, a lawn mower spark plug needs proper care and maintenance to last.
  • If your lawn mower spark plug is bad, fixing this means cleaning or replacing it.

Now that you understand how to tell if a lawn mower spark plug is in bad condition, it would be easy for you to distinguish whether it is causing the problem. Most importantly, you can perform these steps on your own to make sure your lawn mower is well-maintained.

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