How to Change the Spark Plug on a Lawn Mower: Fast and Easy




How to Change The Spark Plug on a Lawn Mower

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How to Change The Spark Plug on a Lawn Mower

 Have you ever gone to mow your lawn, and your mower isn’t running smoothly, or it dies for no apparent reason? It could be many things, but the first thing that I do is check the spark plug. Ninety percent of the time, a new plug will do the trick.

So, how do you change a spark plug? Don’t worry; we have got you covered. This step-by-step guide will walk you through the process and give you a few handy tips on the way. 

Why change a Mower Spark Plug?

When an old lawn mower spark plug is left in a machine for an extended period, it can lead to a poorly performing mower. The performance deteriorates over time, so you may not notice how badly it performs until you change the spark plug. 

Signs that Your Spark Plug Needs to be Replaced

These are the most common signs that your spark plug is on its way out. 

  1. Hard to start: As a spark plug ages, the spark gets weaker, and it becomes increasingly harder to start the mower. If you have to pull your starter cord half a dozen times to get your lawn mower started. It’s probably the plug. 
  2. Poor fuel efficiency: If you notice that you are using more fuel, that is also a sign of a spark plug that could be past its use-by date. An old plug can cause incomplete combustion in the engine, wasting fuel and increasing consumption. 
  3. Engine misfires: Older spark plugs can inconsistently ignite the fuel-air mixture. This will reduce power and performance. 
  4. Rough idling: A lawn mower should idle consistently. It is time to check the existing spark plug if it is surging and spluttering. 

Now that we have examined the symptoms let’s look at how you would solve the problem. 

Safety Precautions Before Starting. 

Before you start fiddling around with a lawn mower, my first advice is always to disconnect the spark plug cap. However, since that is the item we are removing this time, that is redundant. 

However, if your mower has been running, do remember to let the engine cool down for at least 15 minutes before you start work. Also, take note of where the muffler is and treat it with the respect it deserves if it is hot. 

Have gloves, safety glasses, and earmuffs in case you need them. 

Pulling off a spark plug cap with pliers
Pulling off a spark plug cap with pliers

Tools Required for Changing the Spark Plug

Now it’s time to get the tools you need together to work on the lawn mower. You should have these lying around in your shed. If not, I will attach links to my recommended tools. 

  1. Socket Wrench: It is one of my go-to tools. Make sure you use the correct size socket, and it fits tightly around the spark plug so you don’t slip and damage it. You may need a spark plug wrench if the standard sockets don’t reach. These sockets are longer and specially built to remove spark plugs. 
  2. Spark plug gap gauge: You will need this tool to measure the gap between the spark plug electrodes. When working with spark plugs, you need to set the gap correctly. Getting this right will give you much better performance. 
  3. Spark plug boot puller: This is a tool to remove the spark plug wire safely. I must admit, I have other tools (like a screwdriver) for this particular job. However, using a tool not designed for the job can damage the wire or the rubber fitting if it is used incorrectly. 
  4. Wire Brush: This tool will help remove rubbish and ensure a clean connection when installing the new plug. 

Now that you have everything you need let’s dive in and do it. 

An old spark plug I pulled out of a machine today

Changing your spark plug

Swapping out a spark plug on a lawn mower is quite simple. Here’s a basic breakdown of what to do. 

  1. Prepare the Lawn Mower:
    • As mentioned before, if the engine is hot, let it cool for at least 15 minutes. 
  2. Locate the Spark Plug:
    • The spark plug is typically found at the top of the engine and has a rubber cap covering the end. 
    • If you cannot see the spark plug immediately, you may need to remove an engine cover to access it. This usually is just a few small bolts.  
  3. Remove the Old Spark Plug:
    • Remove the spark plug lead with a Spark plug boot puller or a similar tool. 
    • Make sure you use the correct socket size for the spark plug; it should be a snug fit. 
    • Start turning the plug counterclockwise to loosen it.
    • When it is just about out, carefully unscrew it the rest of the way by hand.
  4. Inspect and Prepare the New Spark Plug:
    • Check the manufacturer’s instructions in the owner’s manual to get the correct gap size for the new spark plug.  
    • Use the spark plug gauge to set the gap. 
    • Add a small amount of anti-seize compound to the new spark plug threads. It’s not compulsory, but it will make it easier to remove the plug next time. 
  5. Install the New Spark Plug:
    • Carefully start screwing the new spark plug into the engine by hand. This will avoid cross-threading. 
    • Once the spark plug is as tight as you can get it by hand, complete the job with the socket wrench
    • Do not over-tighten. Just tighten it enough so you know it won’t come undone. Overtightening can damage the threads or crack the plug’s ceramic insulator. 
    • Insert the spark plug into the engine and hand-tighten it until it’s snug. Be cautious not to overtighten, as this can damage the threads or crack the ceramic insulator.
  6. Reconnect the Spark Plug Wire:
    • Now reconnect the rubber boot holding the spark plug wire back onto the tip. If it is loose, give the rubber boot a light squeeze with some pliers.

Now you are done. Make sure that you hand-tighten the spark plug before using the wrench. I have had a worker ruin one of my engines by tightening it from the start with a wrench and cross-threading the plug without realizing it. 


The Most Common Mistake Made When You Change Spark Plugs

The biggest mistake made is putting the wrong plug into a lawn mower. Several brands have equivalent plugs, but you need to buy the correct plug. You can use a site like sparkplug-crossreference, which will help you find the correct plug. Otherwise, a good old Google search will do the trick. 

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Tips for Maintaining Your Lawn Mower’s Spark Plug

You can increase the performance of your mower’s engine and the plug’s life by doing regular maintenance. 

1. Clean the spark plug regularly: Once every few months, or more often when it’s dry and dusty, removing and maintaining your plug is good. Use a wire brush to clean the carbon buildup of the electrodes gently. 

2. Check the spark plug gap: While you have the plug out, use a spark plug gauge to check the gap and ensure it is still correct. Here is some advice from Briggs and Stratton on setting your gap. 

4. Don’t use cheap fuel: Ensure you use quality fuel in your mower. I once took my mower in for repairs because it was running badly. The workshop technician put his finger in the tank and sniffed it. He then told me exactly what budget fuel place I had used and told me to use good fuel. I did and never had that issue again. 

How Often Should You Replace a Lawn Mower Spark Plug?

A few different factors come into play when looking at how often to replace a spark plug. These are things like the type of plug, what condition your lawn mower is in, and, of course, the manufacturer’s recommendations. 

The general rule of thumb is to replace your plug every 25 to 50 hours of operation or at the beginning of the season. 

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Troubleshooting Spark Plug Issues

If you replace your spark plug and are still experiencing issues, here are other things to check. 

1. Check the spark plug wire: Check that it is connected at both ends and is not damaged or loose. 

2. Check the fuel tank: There could be water in the fuel. Tip the fuel into a clear container, and if there is any water, you will see it at the bottom of the fuel

3. Check the air filter: The easiest way is to remove it and start the mower. If the problem is gone, the filter needs cleaning, drying, or replacing. 

If none of these work, it is time to call in the big guns and take it to a professional. 

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Conclusion: How to Change The Spark Plug on a Lawn Mower

The article offers a guide on replacing the spark plug in a lawn mower, underscoring its significance in keeping the machine running. It starts by pointing out signs indicating when a spark plug replacement is needed, like starting troubles, decreased fuel efficiency, engine misfires, and uneven idling.

The step-by-step process of changing the spark plug is explained thoroughly, including prepping for finding the spark plug location, taking out the one examining and readying the plug, and fitting it correctly. Safety measures and essential tools are also addressed.

Moreover, helpful pointers on prolonging the spark plug’s lifespan and troubleshooting problems are provided. The article wraps up with advice, on how to replace the spark plug and when professional help might be necessary.

Frequently asked questions

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