Should A Lawn Mower Spark Plug Be Wet?

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Should A Lawn Mower Spark Plug Be Wet?

No, a lawn mower spark plug should not be wet. If you notice your spark plug is wet, it is an indication that something is wrong somewhere. It can either be with your engine, the spark plug, or with the way you operate the lawn mower.

Even though a wet plug doesn’t mean your engine will blow up when you start it, it can result in long-term damage if the problem is not resolved as soon as possible. 

What Happens When Your Lawn Mower Spark Plug Is Wet?


Whether wet with gas, oil, or water, a wet plug is likely going to misfire. Because of that, the current typically flows over an insulator because the gas, oil, or water conducts it instead of passing through the gap.

Most times, this may require you to use more effort to start the engine and can damage other parts of your mower. 

Why Is My Spark Plug Wet With Fuel?


There could be various reasons for a spark plug to be wet with fuel. And when it happens, you need to either take the plug out and properly clean it or replace it with a new one.

However, before you clean or replace your wet spark plug, it is best to know why the plug was wet in the first place. So, you can do something about it. The most common reason is due to engine flooding or injector leak.

Engine flooding


Engine flooding is most common during freezing weather conditions. During this time, it can be a bit harder to start the engine, especially if the spark plug is not at its best. Trying multiple times to start the engine may cause the engine to be flooded with fuel, making it even harder to generate any spark that can start the engine.

In this case, what you need to do is to allow the plug to become dry or take it out and clean it. Then, reinstall back into the lawn mower.

Injector leaks

This is one of the most common issues that may happen to your lawn mower engine that can result in wet fouling. Cold start injectors can leak, especially in older lawn mowers.

When this happens, the engine compartment will likely be filled with a rich starting mixture, causing the spark plug to foul. Also, removing the plug, cleaning it properly, and reinstalling it will fix the issue.

Why is My Spark Plug Wet with Oil?

The spark plug is usually wet with oil when the plug has overheated, and the combustion chamber is flooded with oil. This can make it pretty hard to start the engine. Over time, trying hard to fire up your mower can cause long-term damage to the engine.

So, coming back to why this happened in the first place; below are some reasons:

Long overuse of a spark plug

The way spark plugs are designed, they are not made to last forever. They should be changed at least every two years, or after 25 hours of use. If your spark plug is due for a change, it may become harder for it to produce the necessary spark to start the engine. Trying too hard can flood the engine.

Excessive usage of the choke

You may have used the choke too much, which then introduced too much fuel into the system. Also, make sure you don’t over-prime the mower. Primers are only designed to improve combustion and freshen up gas.

Stuck issue with the float

Check and be sure your float is not stuck in the down position. When this happens, it won’t be able to control the amount of fuel that leaks into the engine. It can cause fouling in the long run.

What Happens If Water Gets In A Spark Plug?

Your spark plug can get wet when water gets into it. It causes your lawn mower to suddenly start firing inappropriately while moving or even stop altogether. Furthermore, when water continuously gets to the plug, it can increase the chance of having its head cracked or blown in the future.

The rule of thumb is to never leave your lawn mower out in the rain. Rain can get into the spark plug compartment or even into the fuel or oil, causing the mower not to start.

At the same time, mowing wet grass early in the morning with dew or shortly after rain can cause water to flood the plug compartment.

Is This What I Can Fix Myself Or I Need to Take It to a Technician?

Well, if you are comfortable with a repair, the issue is what you can fix on your own. But remember that the first, and most important step is to determine the actual problem of the plug and the best way to fix it.

This may mean going to your local lawn and garden store to get some things you will need. But you can be sure it will save you some money in the end.

However, if you have some extra buck to spare, it is recommended you take the mower to a technician to help examine and fix the problem. A technician will also have all the tools and equipment needed to get the job done. Plus, it doesn’t take time at all.

But if you want to do it by yourself and save some cash, below are some quick fixes to consider.

How to Fix a Wet Lawn Mower Spark Plug

Step 1: Clean and dry the spark plug

First thing is to take out the plug – you will need some tools to do this. Then, properly clean the plug and let it dry. Now reinstall it back into the compartment. But if the engine won’t start, proceed to the next step.

Step 2: Use starter fluid

Get a starter fluid. Remove the air filter of your lawn mower and spray the fluid down the carburetor. Make sure you turn off the choke before doing this. Now, try to start the mower.

If it starts, turn it off again, and clean off the air filter very well before reinstalling it back. But if the engine did not start after spraying some starter fluid, move on to the next step.

Step 3: Replace the oil and gas

Drain the oil and gas. But be careful when doing this so you don’t incur any danger to yourself. Don’t do it near any form of flame or when the spark plug is intact.

A safe way to drain the gas or oil is to disconnect the oil/fuel line and drain it into a bucket. On the other hand, you can use a fuel transfer pump.

Replace the gasoline or oil with fresh ones and try to start the engine again. If this still won’t start the engine, you may need to replace the spark plug.

Step 4: Replace the spark plug

Check online for a new spark plug or head to your local lawn and garden store to get one. Spark plugs aren’t expensive, so even if you are buying one, you are still saving a good deal of money.

Once you get the new spark plug, install it into the mower and try to start the engine. If it won’t start, move on to the next step.

Step 5: Clean the coil and magnets

Turn off the fuel valve and check for any sign of rust on the coil. If it’s dirty, get sandpaper or a rough brush to clean it. Also, clean the magnets on the flywheel. Reinstall the coil and be sure you tighten it back into its original position.

How Can I Prevent This From Happening In The Future?

  • Don’t leave your lawn mower out in the rain, so water doesn’t get into the plug compartment or in the fuel.
  • Don’t mow your lawn after rain or when the grass is wet.
  • Don’t over-prime your lawn mower.
  • Change oil annually or after 50 hours of use
  • Replace the plug after 25 hours of use


Now that you know it is not okay for a lawn mower spark plug to be wet, you should take action the next time you notice it on your plug. We already talked about different reasons this can happen, as well as possible fixes for the issue.

However, remember that while drying or cleaning the plug can temporarily fix it most times, the best way is to address the main cause of the problem. If you think you are not comfortable with getting it done yourself, you can take your mower to a technician to fix it for you.