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Will Mower Run Without Air Filter? (don’t do it!)

By: Author John Cunningham. Published: 2020/12/17 at 12:45 pm

Last summer, a customer came into my shop with a nonrunning mower; I noticed it didn’t have an air filter fitted. I enquired, and what he told me made me fear the worst for his little mower. He said, “The air filter fell off about two seasons ago.”

A mower engine will run without an air filter. However, prolonged use without the air filter risks damaging the piston and cylinder.

By the end of this post, you’ll understand why running your mower without an air filter is a costly mistake in the making.

Mower Air Filter Function

Sure, your mower will run without the filter, and if your old filter is clogged with grass, dust, and debris, the mower will run even sweeter without the filter.

Air filter

The main function of the air filter is obvious: it prevents grass, dust, and grit ingestion.

The filter also settles and uniforms airflow over the carburetor’s mouth. Even steady airflow makes for a smoother-running, more powerful, and efficient engine.

Risks Of No Air Filter

It is very tempting to run a mower without the filter, especially as it may run great without it, but it comes with real risks. The problem is that fine rock particulars known as silica are ever-present in the air. Prolonged mower use without a filter will cause the silica particulars to erode the carburetor, valves, piston, and cylinder.

Engine wear

Silica acts as a sandblasting media, eroding everything it comes in contact with.

Problems won’t arise initially but will eventually take their toll. How much damage depends on silica levels, how much and often you mow.

How Often Should I Clean Mower Air Filter?

A paper filter should be cleaned every 50 hours of operation and more often if conditions are dusty. Replace the filter every 100 hours of operation. Clean a sponge filter every 50 hours of operation and, more often, in dusty conditions. There is no need to replace a sponge filter unless it’s torn or disintegrating. Sponge filters usually last years.
Check out my post on mower tune-up, it covers everything you need to know to take care of your own tune-up. Or, if you need video help, check out the video library, it covers all the common mower repairs and maintenance chores.

Can I Clean Mower Air Filter?

Accessing air filters is easy; all modern mowers use toolless access. The most common type are fasteners are the plastic push tabs at the top of the air filter cover. Air filters come in two main flavors: sponge or pleated paper.

Sponge Air Filter

Sponge filter

Sponge Filter – The sponge-type filters may be washed in fresh gas, rinsed, and allowed to dry out. Sponge-type filters are often oiled to help trap dust and grit.

Not all sponge filters are treated in this way; refer to your mower manufacturer’s recommendations.

Pleated Air Filter

Pleated Paper Filter – Pleated paper filters may not be washed in gas or water. Washing this type of filter will prevent airflow through the filter, even after allowing it to dry out.

Paper air filters
Cleaning paper air filter

The best way to clean a pleated paper filter is with compressed air; tapping it on a solid surface also helps knock heavy debris loose. A clean paintbrush also helps remove grit.

Pre Filter

Some mowers that use pleated paper filters may also use a pre-filter. The pre-filter traps larger particles and helps keep the main paper filter cleaner for longer. Not to confuse issues, the pre-filter is usually made from foam, so it (pre-filter) may be washed in gas and allowed to dry out.

Pre air filter

Pre Filter – Pre-filters are sponges and may be washed in gas. Pleated main filters may not be soaked with water or gas.

Should I Oil Mower Air Filter?

Oiling the air filter using engine oil helps trap finer dust particulars, but not all filters may be oiled. Never oil a pleated paper air filter. Oiling this type of filter will partially or completely block the filter, causing your mower to blow black smoke or stall the mower altogether, a condition known as flooding. Check out the how-to unflood mower engine video here.
Oiling a sponge-type filter is generally acceptable, but check with your mower manufacturer first. 

Fitting A Mower Filter

Mower air filter location

Fitting a mower filter is easy; the filter housing is located on the side of the mower, nearly always on the opposite side to the muffler.

Most modern mowers use tool-less air filter covers; pressing the cover tabs releases the cover. Remove the old filter and, using a clean rag wipe the cover clean and the housing. Replace the filter and fit the pre-filter if applicable.