Can you run lawnmower without an air filter?

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Lawnmowers are powered by engines and just like any other gasoline engine, they need a mixture of clean air and fuel in order to run. 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 which is possible with the help of an air filter that 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? 

A lawnmower should never be run without an air filter because without a filter in place, and your engine will suck in debris and harmful particles along with the air. Not to mention that your lawnmower will be sucking in too much air, which is going to upset the air-fuel ratio for your lawnmower’s engine. If you absolutely have to run a lawnmower without an air filter while trying to diagnose a problem or when troubleshooting, make sure to do it when the lawnmower isn’t moving. Because when the mower is stationary and surrounding air is clean there are fewer chances of debris entering the engine of your lawnmower.

The air filter is an important component of your lawnmower that is why cleaning or replacing the air filter is a part of regular maintenance routine for any lawnmower with a gasoline engine. And in this article, we are going to explain why it is a bad idea to run a lawnmower without an air filter and how you can properly replace or clean the air filter of your lawnmower.

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

When you run your lawnmower without an air filter, you are doing many harmful things to your mower’s engine indirectly. Here are some common problems you will run into if you use your mower without an air filter.

  • Reduces the life of 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 and it is meant to move in a closed cylinder and should never come in contact with any debris or other external particles. But as soon as unfiltered air containing dirt and other debris comes in contact with the piston is starts to damage it and you run a risk of premature wear of the engine and even complete engine failure of your lawnmower. 
  • Lack of power from the mower: Since lawnmowers have small engines they are not meant to produce a lot of power, to begin with. But 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, which means the engine will run lean and the engine will not get the required amount of fuel to perform efficiently. As a result, you will have a hard time mowing the lawn, and the engine might 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 required to turn over the engine and start it up. But if there is no air filter present, the air will rush into the engine of the mower way too quickly and the mower will fail to start. Or even if the engine does start, it will fail to idle or keep shutting down.

No good will come by running your lawnmower without an air filter, and since the air filters for lawnmowers don’t cost a lot of money, it is not wise to let a lawnmower run without an air filter. In addition to being cheap lawnmower air filters are very easy to install as explained in the next section of the article.

How to install or replace a lawnmower air filter? 

Installing an air filter in a lawnmower is a pretty straight forward task and in some cases, you won’t even need any tools to install a new air filter. But before you do anything you will need a brand new air filter to install in your mower and you should get the air filter that is designed for your lawnmowers make and model for it to fit inside your lawnmower. You can install an air filter into your lawnmower by following these simple steps:

Step 1. Locate the spark plug wire and pull it out 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 and turn on the mower as you work on it. 

Step 2.  Next, you have to locate the air filter housing and 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 up the air filter cover by undoing the clips or screws and inside you will find the space where the air filter is meant to be installed. There is also a pre-cleaner made out of foam that is located inside the cover you take off when opening the air filter housing along with the main air filter. So if your mower is missing the pre-cleaner you will have to install it as well. Pre-cleaners are usually made of foam and last longer than the main air filter. 

Step 4. Clean out the air filter cover and air filter housing as there can be some debris in there as well. Next, make sure that the air filter and the pre-cleaner you have bought fits inside the air filter housing perfectly. 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 air filter housing and make sure that the cover is properly dried before putting it back on.

Step 5. Take the pre-cleaner and place it inside the cover and fix the air filter inside the air filter housing making sure that the flat end of the filter is pointing inwards towards the engine and the pointy end or the end with the hole for the screw is pointing outwards towards the cover of the air filter housing. 

Note: You would want to make sure that the filter has been installed snuggly and there are no spaces for air to pass into the engine without going through the air filter first. Because if there are gaps or the filter is not fitted properly unfiltered air can still pass into the engine and damage it.

Step 6. 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 in it and cleaning it up

Note: One thing you have to be careful about when tightening the screws of an air filter is not to tighten them up too much. Because most covers are made out of plastic trying to tighten them up excessively can crack the cover and it can be difficult to find a replacement air filter housing for a lawnmower. 

Some types of lawnmowers have no pre-cleaner foam so in that case, you will have to simply replace the air filter itself.

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 because their material is washable and doesn’t get damaged by water. Here is how you clean a washable lawnmower air filter using water.

Step 1. Use the method explained above to take out the air filter from the air filter housing and make sure the spark plug wire is disconnected. 

Note: Examine the air filter after taking it out to make sure 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 the air filter because it is too worn out to be used and can damage your lawnmower’s engine.

Step 2. With the air filter out, shake off any heavy debris from the surface of the filter and 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. Rinse the air filter foam under warm tap water and get it soaked in water. Get some liquid dishwashing soap to wash the air filter because they are good at getting rid of grease and since air filters contain oil that catches dirt particles that pass through it, therefore, dishwashing liquid is ideal for getting all the debris out of the air filter along with the grease. Squeeze the air filter after applying dishwashing liquid to it make sure it gets to every part of the filter. Rinse the air filter to wash away the loose debris 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. Now dry out the air filter 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 and there is as little moisture left in it as possible. 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 in it.

Step 5. As we mentioned earlier washable lawnmower air filters contain oil to catch dirt and debris from the air in order to prevent any particles from entering the engine. Therefore you will have to apply 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 on 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 if you don’t have a pair of gloves available. 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. 

Step 6. Place the air filter back into the air filter housing of your lawnmower in the same way as you took it out and secure the cover onto the air filter.   

If you use your lawnmower in extra dusty conditions then you will need to clean the air filter often and after reusing the air filter a few times it starts to fall apart that is when you should buy a brand new air filter. 

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 and the pre-cleaning foam can last up to 100 hours with regular cleaning. But even if you are not using your lawnmower too often it is still a good idea to replace the air filter every season to be on the safer side. While there is a recommended time limit 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 so to make up for the lack of air supply the lawnmower’s engine will use more fuel and the fuel efficiency will be reduced. So if your lawnmower is using too much fuel all of a sudden you might want to take a look at its 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 due to 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. That is why it is important to check on your lawnmower’s air filter regularly to avoid running into any unexpected issues.

Conclusion

The air filter is a very important component of your lawnmower’s engine and 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 that is why you should never run your lawnmower without an air filter in place. Similarly, a dirty air filter also restricts air supply to the engine so regular cleaning and replacement of air filters will keep your lawnmower running solid for years.