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Lawn Mower Bad Spark Plug Symptoms: Identifying and Fixing

Are you experiencing problems with your lawn mower? Our team has a wealth of experience in diagnosing and fixing such issues. We can guide you through the steps to identify and fix the problem, ensuring your lawn mower is back in action as soon as possible.

A bad spark plug in a lawnmower causes hard starting, poor performance, stalling, misfiring, and increased fuel use. Check the gap, and clean or replace the plug. Use the same type and gap. Remove the wire, unscrew the old plug, insert the new plug by hand, fully tighten it with a wrench, and reconnect the wire.

Has your lawn mower been rugged to start or performing poorly? These could be signs of a bad spark plug. Our expert team has compiled a guide to help you identify and fix the problem. Follow our step-by-step instructions to get your lawn mower running smoothly again.

What does a Spark Plug do

Though a spark plug is relatively small, it plays a vital role in a gasoline-powered engine. The spark plug in a lawnmower’s engine performs the same job as in an automobile engine. Unlike most parts of an engine that perform mechanical roles, a spark plug is an electrical device.

Its central electrode receives a high voltage from the ignition coil or the magneto. That’s why it is the live electrode. The side electrode doesn’t receive voltage from any source and is a ground electrode.

When a high voltage is provided to the central electrode, a high potential difference is created between the two electrodes, which allows a spark of current to flow between the electrodes. The spark plug is fitted in the engine cylinder head, and the spark ignites the air-fuel mixture.

Combustion of the air-fuel mixture provides energy for the engine to run. If the spark plug cannot do its job correctly, there will be no ignition or improper ignition, causing all sorts of problems. In the worst case, your engine might not start at all.

Symptoms of a Bad Spark Plug

You know the main symptoms now; let’s get into their details so that judging becomes more comfortable for you.

● Engine Has Trouble Starting:

As said, it is the most common symptom of a faulty spark plug. An engine with a bad spark plug won’t start usually. If you are using a push mower, it will take many pulls on the starter rope before the engine starts.

Likewise, a single key turn won’t be enough to start the engine if you use a lawn tractor. Now that you know what a spark plug does, explaining this symptom becomes relatively easy. A faulty spark plug generates a spark too weak to ignite the air-fuel mixture coming from the carburetor.

In my 20 years of experience, I’ve found that difficulty starting the engine, poor performance, increased fuel consumption, and misfires are common symptoms of a bad spark plug in a lawn mower.

As more mixture enters the cylinder and only a tiny portion gets ignited, the engine gets flooded by the entering mixture.

● Bad Performance:

Even if the engine with a faulty spark plug finally starts after many tries, it will fail to keep running for an average period. Because the spark plug is not functioning correctly, the engine will die out immediately or stop mowing.

When the engine keeps dying out, it needs to be repeatedly started. After each try at starting the engine, starting becomes more difficult as the engine gets warmer. This is because heat causes expansion in metals, which widens the gap between the two electrodes, and the strength of the ignition spark further decreases.

Other performance-related problems associated with a faulty spark plug may include the engine sputtering, popping, or missing. Misfires cause these problems.

● Unusually High Fuel Consumption:

If your lawnmower takes more fuel for the same job than usual, one reason might be a bad spark plug.

With a bad spark plug, ignition is inefficient, and the fuel is not combusted correctly. This decreases the fuel efficiency of the mower, thereby increasing fuel consumption.

Another way to judge that your mower is not burning and consuming fuel efficiently is odor. Because of a bad spark plug, the fuel is not burned correctly, and raw gasoline is created as the mower is in operation.

Checking the Spark Plug:

A faulty spark plug will give you clear enough symptoms of the problem, but you don’t necessarily need to wait for the signs. You can check the spark plug periodically so that you are always aware of your mower’s spark plug health.

There are several criteria on which you can judge the health of your spark plug. Once you know your spark plug is not in perfect condition, you can fix or change it.

● Understanding Problems:

Stay informed about an engine’s problems if the spark plug is bad. You can learn about these problems from the user manual or easily from the internet.

If the engine is not starting at all or not starting correctly, immediately check the spark plug. If the engine shuts down during operation, check the spark plug. If you are forced to add fuel, check the spark plug repeatedly.

The best way to check the condition of a spark plug is to remove it and inspect it visually. Over the years, I’ve found that looking for cracks, deposits, or wear can tell you a lot about the health of your spark plug.

● Spark Plug Gap:

The spark plug gap is the gap between the two electrodes. The gap of the spark plug must be proper. Even a tiny deviation from the designated width can cause problems. During operation, the engine becomes hot, which causes expansion and increases the gap.

When the engine is cold, contraction occurs, and the gap reduces. Over time, the electrodes develop residual stresses and strain, and the gap is permanently distorted from its correct width. The wrong gap reduces ignition strength.

Due to this reason, you should let the engine cool down a bit if you’ve been trying to start it repeatedly and let the gap.

– Understanding the Spark Plug Gap

The spark plug gap can also change during shipping or handling if the plug falls on the floor or if the anode gets thinner. So, always check the gap before installing a spark plug.

The spark plug gap is something that can be adjusted. If your engine has a problem starting, check if the spark plug gap is correct. If not, change it to match the spark plug packaging or the engine manual’s gap specification.

When should you change the spark plug of a Lawnmower?

According to experts, a home-owned lawnmower’s spark plug must be changed once per season or after 25 hours of operation.

An acceptable practice can be to be cautious about the problems and change the spark plug as soon as any problem appears.

To stay safe and avoid any problems, changing the spark plug once a year is exemplary.

Cleaning the Spark Plug:

If the spark plug is corroded too badly or has carbon burns or burnt deposits, all you can do is change it. But if the spark plug is wet from too much gas or oil buildup, it can be cleaned.

The live electrode (central electrode) should have a flat surface at the top. If its top surface is damaged, the spark plug should be changed. If there are any cracks on the spark plug’s porcelain sheath, the spark plug needs to be changed.

The plug can only be cleaned if it is wet from gasoline or oil and there is no visible physical damage.

Replacing the Spark Plug:

The spark plug in a lawnmower is located under the black spark plug wire. Disconnect the wire and take the plug out for inspection.

Follow these steps for replacing a spark plug:

● Step 1: Get a similar Spark Plug

Ensure the replacement plug is the same size and with the exact specifications as the one being replaced.

● Step 2: Disconnect the Spark Plug

Disconnect and clean around the spark plug wire.

In my experience, spark plugs should generally be replaced every season or after 25 hours of use. However, this can vary depending on the specific model of the lawn mower.

● Step 3: Remove the Spark Plug

Take the plug out using a wrench and inspect the electrode for any signs of engine problems. If it’s too dry or wet, the carburetor might have a problem.

● Step 4: Put the new Spark Plugin

Put the new plugin by first turning it in by hand to ensure you don’t cross-thread. Use the wrench for further turning when it can’t be turned by hand.

● Step 5: Reconnect the Spark Plug wires

Connect the spark plug wire back.

Final Remarks:

A faulty spark plug can cause problems to the lawnmower engine, making it almost impossible to operate. But if you have basic knowledge of a spark plug’s function, how it works, and the symptoms of a bad spark plug, the problem can be easily solved.

Issues like a distorted gap and the electrode being wet can be fixed, while if there is any physical damage to the plug, it has to be replaced.

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  1. Roy Ford says:

    Great video resources shared in the article! It’s helpful to see the process visually.

    • Allard Vdhooft says:

      Thank you, Roy! We’re glad you found our video resources helpful for diagnosing lawn mower issues. Feel free to reach out for more tips or assistance.

  2. Lawrence Armstrong says:

    Thank you for explaining the science behind how a spark plug works. It was fascinating to learn about.

    • Allard Vdhooft says:

      Thank you, Lawrence! We’re glad you enjoyed the explanation. If you ever need help with your lawnmower, feel free to reach out for expert assistance.

  3. Christian Brewer says:

    The insights provided in this article will help me keep my lawn mower running smoothly. I’m grateful for the guidance.

    • Allard Vdhooft says:

      Glad to hear that the article was helpful! Remember, our team is here to guide you through fixing any issues with your lawn mower. Happy mowing!

  4. Kristina Pierce says:

    What tools are needed to replace a spark plug in a lawn mower?

    • Allard Vdhooft says:

      Kristina, to replace a spark plug in a lawn mower, you will need a wrench and a new plug of the same type. Follow our step-by-step guide to ensure your mower runs smoothly again.

  5. Violet Harris says:

    This article was very informative and helpful! Thank you for sharing the tips on spark plug maintenance.

    • Allard Vdhooft says:

      Thank you for your kind words, Violet! I’m glad you found the article helpful. If you need further assistance with spark plug maintenance for your lawnmower, feel free to reach out. Happy mowing!

  6. Jamie Burton says:

    As a beginner in lawn mower maintenance, this article was a great starting point for understanding spark plug issues. Thank you for the clarity.

    • Allard Vdhooft says:

      Thank you for your kind words, Jamie! We’re glad our article helped you understand spark plug issues. If you need further assistance with your lawn mower, feel free to reach out to us.

  7. Stella Spencer says:

    Can a spark plug be cleaned with household items?

    • Allard Vdhooft says:

      Yes, a spark plug can be cleaned if wet with gasoline or oil. If corroded or damaged, it should be replaced to ensure proper engine function and performance.

  8. Charles Dunn says:

    Is it dangerous to replace a spark plug on a lawn mower without proper knowledge?

    • Allard Vdhooft says:

      Hi Charles, replacing a spark plug on a lawnmower without proper knowledge can be risky. Follow our guide for step-by-step instructions to ensure your mower runs smoothly.

  9. George Vargas says:

    The step-by-step guide on checking and replacing a spark plug was easy to follow. Thank you for the detailed instructions.

    • Allard Vdhooft says:

      Thank you, George! We’re glad you found the guide helpful. If you have any other lawnmower issues, feel free to reach out. Happy mowing!

  10. Jessica Mendoza says:

    What are the signs that indicate a spark plug needs to be replaced?

    • Allard Vdhooft says:

      If you’re experiencing hard starting or poor performance, it may be time to replace the spark plug in your lawnmower. Check our guide for more information!

  11. Elsie Harris says:

    I appreciate the information on the symptoms of a bad spark plug. It will help me troubleshoot issues with my lawn mower.

    • Allard Vdhooft says:

      I’m glad the information was helpful to you, Elsie! If you run into any issues while troubleshooting your lawn mower, feel free to reach out for assistance.

  12. Craig Ward says:

    I never realized how much impact a spark plug could have on the performance of a lawn mower. Thank you for highlighting its importance.

    • Allard Vdhooft says:

      Thank you for reading our blog post, Craig! If you need further assistance with your lawn mower or have any questions, feel free to reach out to our team.

  13. Marilyn Walters says:

    Are there any specific brands of spark plugs recommended for lawn mowers?

    • Allard Vdhooft says:

      Hi Marilyn! For lawn mowers, it’s best to stick to the same type and gap of spark plugs recommended by the manufacturer. Make sure to check periodically and replace as needed.

  14. Daisy Fowler says:

    I never knew how important the spark plug was for a lawn mower. This article was very enlightening.

    • Allard Vdhooft says:

      Thank you for the feedback, Daisy! We’re glad the article helped you understand the importance of a spark plug in a lawnmower. Don’t hesitate to reach out if you need any more assistance with your lawn mower.

  15. Jeff Rodriquez says:

    How often should the spark plug be replaced?

    • Allard Vdhooft says:

      You should replace the spark plug in your lawnmower once per season or after 25 hours of operation to ensure optimal performance. Follow the steps outlined above to do so.

  16. Raul Chavez says:

    Does the type of fuel used in the lawn mower affect the spark plug?

    • Allard Vdhooft says:

      Yes, the type of fuel can impact the spark plug in your lawn mower. Make sure to use the same type and gap for optimal performance.

  17. Carla Butler says:

    Are there any preventive measures to avoid spark plug issues in lawn mowers?

    • Allard Vdhooft says:

      Regularly checking and cleaning/ replacing spark plugs can prevent issues in lawnmowers. Follow these simple steps to maintain your mower’s performance.

  18. Dean Cooper says:

    Is it necessary to check the spark plug even if the lawn mower is working fine?

    • Allard Vdhooft says:

      Regularly checking the spark plug is crucial for maintaining optimal mower performance. Prevent potential issues by ensuring the spark plug is in good condition.

  19. Marjorie Wilson says:

    Can a bad spark plug damage the engine of the lawn mower?

    • Allard Vdhooft says:

      A bad spark plug can indeed damage the engine of a lawnmower. Follow our guide to diagnose and fix the issue to get your mower running smoothly again.

  20. Leroy Bryant says:

    This article has inspired me to be more proactive about maintaining my lawn mower’s spark plug. Thank you for the valuable tips.

    • Allard Vdhooft says:

      Thank you for sharing your experience, Leroy! We’re glad our tips could help you maintain your lawn mower. Remember, regular spark plug maintenance is key to ensuring smooth operation.

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