When to Change Spark Plug on Lawn Mower?

Spark plugs are one of the most important components of an internal combustion engine. However, not many people realize it can cause serious issues to your engine performance if not replaced on time. 

This brings about the question of when to change spark plug on lawn mower? Spark plugs of lawn mower must be changed when it has an adverse effect on the performance. Most manufacturers design spark plugs for a maximum of two years. To ensure optimum engine performance, changing the spark plugs once every year or after 30 hours of use is a good practice.

Read on as I explain this answer in detail, while also talking about spark plugs in general. This includes information on cleaning and knowing when your spark plug has gone bad. 

Disclosure: Some of the links below may be affiliate links.

How do I know if my lawn mower spark plug is bad?

When your engine has bad plug sparks, it will affect the ignition of the fuel. This will be a major reason why you have to tug at your start rope multiple times to get your lawnmowers started.

The engine will not have enough heat of its own to keep the combustion process running, resulting in the engine sputtering and failing to start.

So, How do I know if my lawn mower spark plug is bad? Your spark plug is bad when you face one or a combination of the following issues

  • Difficulty in starting
  • Engine dying out quickly after starting
  • Poor fuel efficiency

When you somehow manage to start your engine, you will still have the engine dying out on you the first couple of times. This is because of the lack of heat in the engine, which together with spark plugs cannot sustain the ignition process unless the fuel mix is rich with fuel, allowing for easier ignition.

While a fuel-rich mix helps reduce the severity of bad spark plugs, it could result in your engine drinking up more fuel than it should. This will result in your lawnmower having poor fuel efficiency, increasing your gas bills as a result.

How long do spark plugs last in lawn mowers?

Most spark plugs are designed to last for a maximum of 30 hours of use, or one season. Or you can read the manual of your lawn mower to find out the exact time of how long do spark plugs last.

Many people make the wrong assumption that spark plugs in lawn mowers are designed to be built for longer than that, like those in a car. The engines in a lawnmower are primarily air-cooled, and smaller in size and it always runs on high RPMs, or in its full capacity, which results in a much more heat being contained in the engine over extended periods of use. 

As a result, the spark plugs wear out much more quickly than those in automobile engines. However, many users have noticed a considerable drop in performance after the first year of use, especially if it is used after long storage during the winter.

What happens if you use the wrong spark plug in a lawn mower?

According to NGK, the world’s leading manufacturer of spark plugs, using the wrong spark plug can result in low ignitability within the cylinder. This causes the improper combustion of fuel, which can cause a reduced output of power as well as reduced fuel efficiency. Eventually, your engine will misfire. 

— Also read: How to Fix a Backfiring Lawn Mower & How to AVOID it?

Spark plugs are designed for very specific engines. They are designed for specific engines, depending on the dimensions as well as the spark plug gap allowance. As a result, fitting the wrong plug can affect these parameters, which then has an adverse effect on the performance of your engine.

Can I clean and reuse spark plugs?

Can I clean and reuse spark plugs

Spark plugs are designed to ignite the fuel and air mix, allowing the engine to create power. Over a period of time, the electrode of the spark plug will be coated in oil, causing it to ineffectively initiate the combustion process. This is called fouling of the spark plugs.

So, Can I clean and reuse spark plugs? Yes, spark plugs can be cleaned and reused. However, this is effective only as a quick fix or in the first couple of times, it is done. But it is not recommended, because if a spark plug is used for more than 50% of its life, then it is better to replace it with a new one. Because you will not get good performance from an old spark plug.

Initially, cleaning the spark plugs will remove the substances coating the electrode, allowing it to function like normal after the procedure. However, you may not receive the same efficiency and power output from your engine compared to when the engine was brand new.

— Also read: What is the difference between Lawn mower oil and Car oil?

Over years of use, the spark plugs will wear out considerably, which will further compound the issues caused by fouling. Cleaning the spark will have a minimum effect on your engine performance, as the only proper solution in these cases would be to replace the spark plugs.

How to clean spark plugs?

Pull out the spark plugs from the engine. Air-dry the area around the cylinder to prevent any debris from falling into the engine. Once you have separated the spark plug, clean the electrode using sandpaper.

Use a wire brush to remove gunk and grease from the threads of the spark plug. For tougher gunk that does not get removed with sandpaper, use a blowtorch to melt the carbon of the plug.

Sandpaper is an abrasive surface used in smoothening and cleaning applications. It will help you effectively remove the gunk without scratching or eroding the electrode. A wire brush will give you access to the fine grooves, which cannot be reached by our fingers. 

Blowtorching your spark plugs will not damage them. This is because the spark plugs are designed to withstand explosions in the engine chamber that release extremely high temperatures. As a result, it will be only the carbon-based gunk that has fouled your plug that will melt away.

This brings about another question to many people though. What are the cleaning products that one can use to clean their spark plugs?

Spark plugs can be cleaned using a wire brush and a spray-on plug cleaner. If you do not have these products, you can use a carburetor or brake cleaner to clean them as well. Even WD-40 is an effective way to clean spark plugs. 

The added benefit of using WD-40 is that it provides a layer of electrical insulation while doubling as a lubricant. This will help you insert and remove the spark plugs without damaging the walls or the spark plug itself. 

  • Where is the spark plug on my lawn mower?

If you are facing problems finding the spark plug, then you can check out the manual of your lawnmower, it will have everything for you. The spark plug is located inside the engine of the lawnmower. It can be easily found as the electrical wire connected to the engine is attached to the spark plug.

  • How often should spark plugs be changed?

Manufacturers build spark plugs to last for a maximum of 25-30 hours of usage, or one season, you can check the exact time of your spark plugs from the manual of the machine. Depending on how your engine performs, it is suggested that spark plugs be changed once a year or after 30 hours of use, whichever comes first.

  • What happens if you don’t change your spark plugs?

Not changing a spark plug could cause a degradation in engine performance. You could face trouble while starting your lawnmower or keep it running. Even if you overcome these difficulties, you will have a machine that offers you very poor fuel efficiency.

  • What causes spark plugs to go bad fast?

Spark plugs can go bad faster than they are designed to because of overheating. This happens due to improperly timing on the engine or improper air to fuel ratios. Oil contamination can cause acceleration of the fouling process.

Failure of the seals, resulting in seepage is the most likely cause of this problem. The last reason why spark plugs degrade faster than normal is due to carbon accumulation caused by dirty injectors or a clogged air filter.

  • Do spark plugs go bad with age?

Yes, spark plugs are designed such that a tiny fraction gets worn out every time ignition of the fuel-air mix occurs. The electrode loses a small amount of the electrode which each spark, as it generates a tremendous amount of heat due to the voltage difference of at least 10.000 volts or more. This results in the electrode wearing out over time.

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