Can you run a lawnmower without an air filter?


A lot of Lawnmowers are powered by small gas engines. They use a mixture of clean air and fuel for optimal combustion. Since lawnmowers are exposed to plenty of dirt and debris when they are used it is important that the engine of your mower gets clean and dirt-free air. This is achieved by using an air filter. It filters out any dirt and other particles to provide clean air for your lawnmower’s engine. But what if we run the lawnmower without an air filter? 

Can you run a lawnmower without an air filter?

A lawnmower should never be run without an air filter because your engine will suck in debris and harmful particles along with the air. The amount of air will also be higher and can change the air-fuel ratio. That can lead to your engine running less efficiently. If you have to run a lawnmower without an air filter while trying to diagnose a problem make sure to do it when the lawnmower isn’t moving, as there are fewer chances of debris entering the engine of your lawnmower.

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The air filter is an important component of your lawnmower and needs regular cleaning or replacing. Checking should be part of your regular maintenance routine that has a gas engine. This article will further discuss the reasons why it is a bad idea to use a lawnmower without an air filter, and how you can properly replace or clean your mower’s air filter.

What happens if you run a mower without an air filter?

When you run your lawnmower without an air filter it will probably start and run. But at the same time, you are sucking in small particles that can harm your mower’s engine over time. Here are some common problems you will run into if you use your mower without an air filter:

● Using no air filter reduces the life of your lawnmower’s engine

One of the most important reasons why you should never run a lawnmower without an air filter is because external particles can enter the engine and can damage it. There is a moving piston inside your lawnmower’s engine that moves in a closed cylinder. It should never come in contact with any debris or other external particles. These particles can lead to premature wear and tear of the engine, and eventually to a complete engine failure. 

Lack of power from the mower: 

Since lawnmowers have small engines they are not meant to produce a lot of power. When the air filter is absent from a lawnmower it will cause the engine of the mower to suck in too much air and not enough fuel. This will lead to the engine running lean and running inefficiently. As a result, you will have a more difficult time at times where a lot is asked from the engine. The engine might also backfire and run really slow. 

The lawnmower will be difficult to start: 

When we start the lawnmower a perfect ratio of fuel and air is required to achieve the first combustion. If there is no air filter present, the air will rush into the engine of the mower way too quickly and the mower will be difficult to start. And if the engine starts, it can fail to idle correctly or keep shutting down.

Looking at the different reasons there is no advantage to using your lawnmower without an air filter. Air filters for lawnmowers are generally cheap and really easy to install. The next section of this blog will look at replacing your air filter.

How to install or replace a lawnmower air filter? 

Installing an air filter in a lawnmower is a pretty straightforward task. In some cases, you won’t even need any tools. Before starting you should check that you have the correct replacement for your lawnmower brand and type. If it does not fit well it can leak air and let dust particles through. You can install the new air filter into your lawnmower with the following simple steps:

Step 1: Disconnect the sparkplug cable

Locate the spark plug cables and disconnect them. This is to prevent the accidental startup of the lawnmower while you are installing the air filter. Secure the spark plug wire away from the spark plug to prevent it from coming in contact with the spark plug. 

Step 2: Locate the air filter 

Locate the air filter housing. Most lawnmowers usually have their air filters secured behind a plastic or metal cover. You can find the air filter housing on the side of the engine and it is usually secured using clips, screws, or bolts depending on the model and brand of lawnmower you own.

Step 3: Open the air filter cover and remove the air filter

Open up the air filter cover by undoing the clips or screws. Inside you will find the air filter. Depending on your brand and model you can also find a pre-cleaner made out of foam. It is often located inside the cover you take off when opening the air filter housing along with the main air filter. Not all lawnmowers have a pre-cleaner. But if yours does, check it, clean it, and replace it when needed. Pre-cleaners are usually made of foam and last longer than the main air filter. 

Step 4: Clean the air filter housing

Make sure that the air filter and the pre-cleaner you have purchased fits perfectly inside the air filter housing. Clean out the air filter cover and air filter housing as there can be some debris in there as well. Since most air filter housing covers are made out of plastic you can easily rinse it under running water to make sure there is nothing stuck inside it. Meanwhile, you can use a cloth to clean the inside of the air filter housing. Make sure that the cover is properly dried before putting it back on.

Step 5: Place the new or cleaned pre-cleaner and main air filter in the housing

Take the pre-cleaner and place it inside the cover. Place the main air filter inside the air filter housing. Make sure that the flat end of the filter is pointing inwards towards the engine and the pointy end of the end with the hole for the screw is pointing outwards towards the cover of the air filter housing. 

Note: Ensure that the filter has been installed correctly, and there are no spaces for air to pass into the engine without going through the air filter first. If there are gaps or the filter is not fitted properly unfiltered air can still pass into the engine and damage it.

Step 6: Close the Air filter cover

For the final step, align the clips or screw slots of the cover with the slots on the main air filter housing and tighten them up. You will feel a noticeable increase in the performance of your lawnmower after installing a fresh air filter or after cleaning it

Note: Take care when tightening the screws of the air filter cover. It should be tight, but not too much. Most covers are made out of plastic, and trying to tighten them up excessively can crack the cover. For some older models, it can be difficult to find a replacement air filter housing. 

Some types of lawnmowers have no pre-cleaner foam. In that case, you only need to clean or replace the main air filter.

How to clean a lawn mower air filter?  

Paper-made lawnmower air filters are meant to be replaced because it is not possible to wash them. You can use pressurized air to blow some of the dirt out of a paper air filter but it won’t do much in terms of cleaning up the tiny spaces between the air filter material. But some foam-based air filters can be reused a few times before they need replacement. Their material is washable and if done carefully will not get damaged. Here is how you clean a washable lawnmower air filter using water.

Step 1: Remove and check the air filter

Use the earlier explained method to remove the air filter from the air filter housing. Make sure the spark plug wire is disconnected. 

Check the air filter: Examine the air filter after taking it out. Ensure there aren’t any holes or other visible damage to the air filter that would allow debris to pass through into the engine. If you see signs of significant damage and wear on the air filter you will have to replace it.

Step 2: Remove any dirt from the surface of the air filter

With the air filter out, shake off any heavy debris from the surface of the filter. Gently rub any solid particles off the air filter foam. Don’t pull any grease or other sticky stuff that is stuck on the air filter because there is a risk that you will end up ripping the filter foam by doing so. Any tough debris will be taken care of in the next step.

Step 3: Clean the air filter carefully

Rinse the air filter foam under a warm tap and get it soaked in water. Use some liquid dishwashing soap too because that helps to remove grease. Air filters often contain some oil that catches dirt particles that pass through them. Using dishwashing liquid is even more ideal for getting all the debris out of the air filter along with the grease as it is more powerful than a normal handsoap. Squeeze the air filter after applying dishwashing liquid to it make sure it gets to every part of the filter. Rinse the air filter again to wash and reapply the dishwashing liquid. Keep repeating this process until you get all the debris, dirt, and grease out of the air filter. Once you are sure that the filter is clean squeeze out any water and soap from it.

Step 4: Dry the air filter

Dry the air filter fry by wrapping it inside a piece of absorbing cloth or paper towels and squeezing it so that most of the moisture is soaked from the air filter. Make sure that only a little moisture is left. To completely dry out the air filter foam place it out in the sun for a while until it is nice and dry.

Note: Don’t move on to the next step until you are certain that the air filter is completely dried out and there is no moisture left.

Step 5: Use filter oil

As we mentioned earlier, washable lawnmower air filters often contain some oil to catch dirt and debris from the air in order to prevent any particles from entering the engine. It is a good idea to apply some air filter oil to your lawnmower’s air filter foam before installing it back into the lawnmower. You can either pour some air filter oil directly on the air filter and squeeze it with a pair of rubber gloves, to prevent the oil from getting on your hand. Or you can put the air filter into a plastic bag and pour air filter oil inside the bag and squeeze it. Whatever method you use just make sure that the oil has reached every part of the air filter.    

Note: You should remove excess oil from the air filter foam if you notice that the oil is dripping from the filter. You can remove excess oil by wrapping the air filter inside paper towels and squeezing it so that any extra oil gets removed from the air filter. 

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Step 6: Refit the air filter in the housing

Place the air filter back into the air filter housing of your lawnmower, the same way you took it out. Secure the cover onto the air filter.   

If you use your lawnmower in extra dusty conditions you will need to clean the air filter more often. Expect that after cleaning and using the air filter a few times it starts to fall apart. That is the time you should buy a brand new one. 

When to replace or clean your lawnmower’s air filter

Whether your lawnmower has a paper air filter, a foam-based one, or has a combination of a pre-cleaning foam and the main filter, you should replace it after the regular interval for optimal performance. Most manufacturers recommend replacing the air filter every 3 months or after 25 hours of usage. The pre-cleaning foam can last up to 100 hours with regular cleaning. If you are not using your lawnmower often it is still a good idea to replace the air filter every season to be on the safe side. While there is a recommended period after which you should change your mower’s air filter, there are some other signs you can look for that will let you know when to change the air filter.

Excess fuel usage: 

If your lawnmower has a clogged or overly dirty air filter it will not get enough air in order to run correctly. To make up for the lack of air supply the lawnmower’s engine will use more fuel and the fuel efficiency will be reduced. If you notice that your lawnmower is using more fuel then normally you should take a look at the air filter.

Lawnmower engine runs very rough: 

A telltale sign that your lawnmower needs an air filter replacement is when your lawnmower’s engine isn’t running as smooth as usual. The reason for this can be insufficient air coming into the engine. You may also notice that the engine is struggling to idle, and the sound of the engine may also change when the air filter is clogged with dirt.

Lawnmower engines are tough, and they don’t really give up easily. But if the air filter is completely chocked and no air is passing through, the engine may even fail to start completely. This is why it is important to check your lawnmower’s air filter regularly to avoid running into any unexpected issues.

Final remarks

The air filter is an important component of your lawnmower’s engine. It allows the engine to suck in clean and filtered air. Without a filter in place, your lawnmower will be breathing in all the dirt and debris from its surrounding, and that can ruin your engine after time. A dirty air filter also restricts the air supply to the engine and makes it run less efficiently. Regular cleaning and replacement of air filters will keep your lawnmower running solid for years.

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