June 9

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Should A Lawn Mower Spark Plug Be Wet?

By Anton Schwarz

🌱 Stay-at-Home Gardening Guy

June 9, 2020


Having a lawn mower is great, but it can be frustrating when it fails to work as expected. While there are many reasons your lawn mower may stop working, one of the more common issues may be with your spark plug.

If you are having issues with starting your mower – it could ver well be your spark plug and we are going to give you some things you should be looking at.

It all comes down to knowing what a bad spark plug looks like and that you know what to do when it goes bad.

However, before knowing if the plug should be wet, it is good to know why a spark plug exists and what it does.

What is a spark plug?

In a small engine such as a lawnmower, a spark plug is important because it gives a pathway for ignition to occur which is what helps the engine to start. It is an electric gadget that fits into the cylinder head of the engine and helps the engine to kick-start the combustion process when you switch it on.

The composition is made of three segments:

  • A threaded shank, which allows you to install it in an engine block
  • Firing electrode, which forms an arch above the center electrode
  • Center electrode – this is within a porcelain sheath

As you can probably tell – it is pretty important and if the spark plug is in poor condition or suffers some damage, then you will have issues when you try to start the engine or use the mower.

How can you tell if the spark plug is not in great condition?

When you try to turn on the engine of your lawn mower and it fails to start, you might actually think it is an engine problem. However, the spark plug might be the cause for your lawn mower not starting due to faulty operation or damage.

Some of the reasons that may prevent the spark plug from properly starting your lawn mower can include:

  • The spark that the plug creates is too weak to cause ignition of the fuel, therefore causing poor burning of the fuel.
  • The engine becomes too hot, which weakens the spark
  • Excessive levels of fuel consumption – causing you to refill the tank after every few moments, and you will also notice the smell of fuel in the air as you use the mower

Should the spark plug be wet?

With the signs of a damaged or faulty spark plug in the know, you might have the question: should it be wet in the first place?

The answer is always going to be NO!

While it does not mean the engine will blow up when you switch it on, it can lead to long-term damage if you do not resolve it as soon as possible – both to the spark plug and the engine itself.

In the case of a spark plug that is wet due to gas or water it will have a very high chance of misfiring. This is because the gas or water in question will conduct the currents over the insulator, instead of across the gap.

This eventually leads to you using more effort to switch on the engine, and can damage the other parts of the mower.

Resolving the issue

Quick disclaimer: Before embarking on any of the repairs, make sure to check the operator’s manual for any guidance to help you diagnose the problem and solve it.

The normal process of examining the issue would be to switch off the engine, remove the plug itself and dry it, then check it for sparks by grounding the base electrode on the motor cast.

If you see sparks forming, check the other parts of the system until you see where there are no sparks.

Another way is examining the carburetor throat. If you place some drops of fresh fuel, start it up, and notice that the engine runs out the fresh gas, then you likely have an issue of blockage or bad gas.

The key here is to always stick with fresh gas that is premium quality – it should not contain any ethanol, and should be high octane.

When examining the electrode, you should have a flat top. Anything other than that, such as a rounded top, and the spark plug needs a replacement. In addition, make sure to check for signs of physical damage to the porcelain sheath, such as chips or cracks, and pitting on the firing electrode.

When you want to clean the plug spray, spray brake cleaner on it, and leave for a minimum of 10 minutes. Afterwards, use a clean, dry cloth to wipe it and remove any dust or residue, and feel free to repeat the process two or three times.

The aim here is making sure there are no traces of leakage or dirt on the spark plug – otherwise, the operation of the system will be interfered with. If there is any damage that you did not notice due to the presence of the residue, then you should replace the spark plug.

How often should you replace it?

Many experts will tell you that you should replace the spark plug after approximately 25 hours of use, or replace it once every season (except probably the winter time, since you will not be using it). If measuring the hours you utilize it is a problem, you should monitor the lawn mower closely every time you use it, and see if there are any issues that arise.

Just to be on the safe side though, always change the spark plug after every two years at the most, even if you notice it is still performing well.

In addition, note that the spark plug you replace in the mower must fit the specific model – different mowers will need different plugs, and the wrong one will damage the entire system.

Final Thoughts

For the optimal functioning of your lawn mower, the spark plug has to be in good condition – which means it must not be wet. If you notice that it is wet, you can take various steps to correct the problem, or you can choose to replace the plug itself so that it does not lead to lasting system damage.

Anton Schwarz

About the author

Just a regular guy who likes gardening and taking care of my lawn. Striping my lawn is oddly satisyfing to me, I guess I'm weird.

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