Air filters are essential to keeping the lawn mower engine clean of debris to extend the life of the engine. There are four things an engine needs to run: air, fuel, spark, and compression. I’ll go over the first requirement for an engine to run – AIR. 

The engine must have air, and clean air at that, before you can get the engine to run. A clogged air filter can cause your lawn mower to stop running, begin to smoke, or cause significant damage to your engine.

There are many types and sizes of air filters. With so many types of small engines and filters, I’m going to share some differences in air filters along with how you clean and replace them.

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Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing, or operating.Consult a professional if you don’t have the skills, or knowledge or are not in the condition to perform the repair safely.

Do You Have to Use an Air Filter? 

You may think air filters are expensive and want to save a little money. Your attempt at saving money can end up with you having a hefty repair bill when your lawn mower’s engine is damaged.  

If an air filter is not used in your lawn mower engine, dirt and foreign material can get pulled into your engine causing extensive and sometimes irreversible damage. Dirt can cause damage to the piston, cylinder, and carburetor which can reduce the performance and lifespan of your engine. 

Where is the Air Filter Located on a Lawn Mower? 

The air filter is typically located near the top of the engine above the carburetor. This location allows the engine to pull in clean air. The filter is found behind a plastic or metal shroud (cover) that protects the filter. The filter shroud is most often held on by thumb screws or clips. 

How to Clean Lawn Mower Air Filters 

It is crucial to not let your air filter become so clogged it restricts restrict airflow. When the engine is unable to pull air through the air filtration system, it begins to look for air wherever it can find it, including the crankcase.

The engine becomes starved for air and begins to overheat. If the issue is not caught soon enough, the internal components can begin to melt, and the engine can seize. 

Engines are expensive. Checking, cleaning, and replacing your air filter is a small investment to make to protect your lawn mower. 

For Safety: Before removing your air filter, turn off the engine and remove the spark plug boot. 

How to Clean a Foam Filter on a Lawn Mower 

• Wash the filter with dish soap and water to remove dirt 
• Rinse until the soap is removed. Squeeze the excess water out of the filter and lay it flat in the sun to dry.  
• Once the filter is dry, use filter oil to lubricate the filter. Get it wet enough to be lightly saturated with oil, but not too much where it is dripping oil. It can help to use a paper towel to absorb excess oil. 
• If the foam filter is excessively dirty and has dark spots or tears, you need to replace it. 

How to Clean a Paper Filter on a Lawn Mower 

• Tap the filter to knock the dirt from the filter.  
• Once you have removed as much dirt as you can, hold the filter up to the light. You are checking the filter to make sure you can still see light through the paper element.  If you are unable to see light or find the filter is damaged or covered in oil, it is time to change your filter. 
• Do not use an air compressor to blow air through the filter as this can do more harm than good. Always just tap the filter to dislodge the dirt. 

How to Clean a Foam Pre-Cleaner on a Lawn Mower 

• Wash with soap and water. 
• Lay flat in the sun to dry. 
• You must replace the pre-cleaner if it becomes dry and brittle or has any tears present. 

Lawn Mower Engine Sizes and Filters Used 

Push Mower Engines up to 10 Horsepower 

Small push mowers typically use a very thin small air filter on them. One reason is price, but another reason is the engine manufacturer does not expect this engine to run very long each time the mower is used.

The engine on a push mower does not require much airflow because it is very low in horsepower. 

Type of Filter Used: Thin Small Air Filter  

The air filter used in a push mower’s small engine appears thin and flat.  The filter may be made of paper or of foam. The engine design may also use a small foam pre-cleaner or sponge-type filter in front of the main air filter to act as the first line of defense to keep out the dirt.  

Size of Filter 

A push mower air filter is approximately 5” x 7” in size. 

How Often Do You Change a Push Mower Air Filter? 

Push mower air filters should be changed after 25 hours of use, but you should check the condition of your air filter monthly and change it more frequently if you are operating your push mower in dusty conditions. 

Steps to Clean a Push Mower Air Filter 

Take caution when working near the engine as the engine can be hot. 

• Turn off the engine and remove the spark plug boot to prevent the engine from starting 
• Remove the engine shroud which is usually held on with a thumb screw. 
• Remove the filter being careful not to knock dirt into the intake. Remove any dirt remaining from the air filter housing with a dry cloth.  
• Cleaning a Paper Filter – Tap the filter to knock the dirt from the filter. Hold the filter up to the light. If you see areas of the filter where light does not shine through or the filter is damaged, you must replace it. 
• Cleaning a Foam Filter – Wash the filter with dish soap and water. Squeeze excess water out of the filter and lay it flat in the sun to dry. Once the filter is dry, use filter oil to lubricate the filter so it is lightly covered and not dripping with oil. If the sponge filter is excessively dirty or has any tears, you need to replace it. 
• If your mower is using a foam pre-cleaner, you must replace it if it is torn, excessively dirty, or becomes dry and brittle. You can clean the pre-cleaner with warm soap and water and then lay it flat to dry in the sun. 
• Replace the air filter and pre-cleaner (if your engine uses a pre-cleaner). 
• Reinstall the engine shroud. 

12 to 17 Horsepower Lawn Mower Engines 

When you start to get into larger horsepower engines you will notice the air filter is larger and taller. These types of air filters will have a sponge pre-cleaner wrapped around them.  

Bigger engines do require more air to run and build up horsepower and fuel mixtures. Therefore, the engine has a much larger air filter system than the push mower.

You will see this type of filter more common on a v-twin engine ranging from 12 to 17 horsepower and possibly larger depending on the manufacturer’s specifications. 

Type of Filter Used: Oval Filter  

The air filter is oval in size and will usually have a sponge pre-cleaner wrapped around the main paper air filter. 

Size of Filter 

The filters used on a 12 HP to 17 HP engine will be noticeably larger ranging between 8″ and 10″. They are often round or oval in shape and are about 3″ deep. 

How Often Do You Change a 12hp to 17hp Engine Air Filter? 

Air filters should be changed after 200 hours of use, but you should clean your air filter every 100 hours. Change your air filters more frequently if you are operating in dry and dusty conditions. 

You can clean or replace the pre-cleaner more often to minimize how often you must clean or change your main filter element. Simply clean the pre-cleaner with warm water and dish soap and let it air dry. 

Steps to Clean Your Engine’s Air Filter? 

Take caution when working near the engine as the engine can be hot. 

• Turn off your engine and remove the spark plug boot to prevent the engine from starting 
• Remove the engine shroud, usually held on with a couple of thumb screws or clips 
• Remove the air filter from the housing being careful not to knock dirt into the intake. Remove any dirt remaining from the air filter housing with a dry cloth.  
• Tap the filter to knock the dirt from the filter. Hold the filter up to the light. If you see areas of the filter where light does not shine through, you must replace your air filter. Do not use an air compressor to blow out your air filter. 
• If your mower is using a foam pre-cleaner, you must replace it if it is torn, excessively dirty, or becomes dry and brittle. You can clean it using warm water and dish soap. Let dry in the sun. 
• Place the pre-cleaner around the main paper air filter and place it back into the filter housing. 
• Reinstall the engine shroud. 

18 and Larger Horsepower Lawn Mower Engines 

On a large lawn mower engine or commercial engine, the manufacturer may specify a much larger air filtration system on some of their engine products.

Sometimes engine manufacturers will place a smaller air filter, much like the filters used in the 12 to 17 horsepower engines on these engines to keep the price point low. This is especially true for high-end residential and entry-level commercial mowers.  

Some manufacturers will provide an option to upgrade from a smaller air filtration system to a larger commercial type of system. The bigger air filter really keeps the air clean in a canister-style filter and housing. 

Type of Filter Used: Canister Style  

The air filter is a canister-style paper air filter. It uses an inner air filter for an additional layer of defense against debris getting into the engine. 

Size of Filter 

The filters used on most 18 HP and the larger commercial engines will be larger in size at about 10” long and 4” in diameter. 

How Often Do You Change a Large Commercial Engine Air Filter? 

Air filters should be changed after 250 hours of use, but you should clean your air filter every 100 hours. You may have to change your air filter more frequently if you are using your mower in dusty conditions. 

Steps to Clean Your Lawn Mower’s Paper Air Filter

Take caution when working near the engine as the engine can be hot. 

• Turn off the engine and remove the spark plug boot to prevent the engine from starting
• Remove the air filter housing cap which is usually a cap held on with a couple of clips. 
• Remove the filter being careful not to knock dirt into the intake. Remove any dirt remaining from the air filter housing with a dry cloth.  
• Pull the inner air filter out of the outer air filter. Sometimes the inner air filters can be difficult to remove, but the two filters will separate.  
• Tap the filter to knock the dirt from the filter. Do not use an air compressor to blow out your air filter. 
• Hold the filter up to the light. If you see areas of the filter where light does not shine through or the filter is damaged or extremely dirty you must replace your air filter.
• Place the inner air filter into the outer filter and place it back into the filter housing. 

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