Small Engines Dirty Air Filters are Engine Killers

Published on March 20th, 2015 | by Turner Anderson


Dirty Air Filters are Engine Killers

What Do Air Filters Do?

This isn’t a trick question. The purpose of an Air Filter is to filter the air.

Air must be clean before it mixes with the fuel and burns in the cylinders of an engine.

Unfiltered air contains all sorts of dirt and debris. Think of all the grass and dirt that flies around as you mow your lawn. You certainly wouldn’t want any of those particles to enter the internal parts of your engine.

So what are some symptoms you can detect if your air filter is too dirty?

Symptoms of a Dirty Air Filter

Dirty Air Filter Covered in Oil and Dirt
A lawn mower air filter covered in oil and dirt.

Power Loss

Dirty air filter = decreased airflow = less power

A clogged air filter covered in oil and dirt will smother your engine, not allowing the proper amount of air to burn with the fuel. Less combustion power means less horsepower. If you notice your mower is not maintaining consistent power, check your air filter.

More Fuel Consumption

If you’re not getting as much run time out of your equipment as normal, it may be the dirty air filter that’s causing your engine to consume more fuel.

Your engine is trying to compensate for the loss of performance by burning more fuel.

Starting Trouble

Air, Fuel, and Spark. Without one of these components your engine will never start.

So, if your air filter isn’t providing the right amount of air flow into the mixture, your equipment will stall, surge, and sputter as it gasps for air.

Damaging Effects of a Worn Out Air Filter

Hole in Air Filter
Holes in the air filter allow harmful debris to enter the carburetor.

Dirty air filters can lead to worn out air filters. Holes in the fibrous material or cracks around the edges of the filter may form, allowing the dirt and debris to enter the parts of your engine.

If your engine is exposed to these debris particles, it will cause premature wear to the internal parts of your engine, including the pistons, cylinders, and carburetor.

So what do you think is cheaper, rebuilding/replacing the engine or changing a dirty air filter? Go with the air filter.

When to Clean/Replace Your Air Filter

Dirty vs. New Air Filter
Dirty Vs. New Air Filter Comparison

Clean: Air filters can be cleaned if the entire component is still intact, with no tears or holes in the air filter fibers.

Replace: If your air filter is covered in oil, the fibrous filter material is torn, or there are cracks around the filter, you should replace it.

Replacing your air filter is a job you can easily do yourself, instead of taking it into a repair shop. Read your owner’s manual for any specific air filter replacement recommendations.

So protect your lawn mower, chainsaw, generator, trimmer and any other power equipment from an Engine Killer. Clean or Replace that dirty air filter!

Jack’s Safety Tips: Before servicing or repairing any power equipment, disconnect the spark plug and battery cables. Remember to wear appropriate safety glasses and gloves to protect against harmful chemicals and debris. View our Disclaimer.

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About the Author

is the Internet Marketing Manager at Jack's and the editor of Jack's DIY Center. You'll also find him creating How-To articles, videos, newsletters, and much more.

4 Responses to Dirty Air Filters are Engine Killers

  1. Spencer Folau says:

    My 17.5 HP B & S sputter at full throttle. When the air cleaner is removed, the engine won’t start. Any suggestions?

    • Doug says:

      Its likely the choke mechanism is dirty and sticking in the choked position after the throttle is returned to the run position. With the engine off, move the throttle lever between run and choke until you locate what this affects on the engine by the movements it causes. A wire rod with a long loop on its end and attached to the carburetor. It is the choke actuator and gets pushed forward when you move the throttle to the choke position. When you return to run it should also return by light spring tension from the carburetor assembly. With the throttle lever at idle position I simply use my finger to push the rod forward with light pressure and see if it pops back easily when I let go. If is doesn’t, the choke is sticking closed because the shaft it pivots on inside the carburetor inlet is dirty. If the rod you are messing with is under heavy spring pressure you might be on the governor rod next to and behind the choke rod; keep looking for the rod that is attached on one end to the carburetor but free on the other end.
      If you have the rectangular “D” style air filter, remove the air filter cover and look down the carburetor air inlet. If you see dusty grit inside there then the air filter gasket is not sealing properly and leaking dust past the filter (assume they all do). You may be able to get the choke freed up with some spray carburetor cleaner temporarily. For a more reliable fix you’ll need to remove the brass choke plate along with the plastic shaft it assembles to. This requires the engine cover to be lifted and the air inlet to be removed along with the choke assembly which requires close attention to detail. Use a Q-tip to clean the hole the shaft fits into and reassemble it being sure to get the little return spring in correctly. Then, very important, apply a 1/4 inch wide by 1/16 inch thick bead of RTV Silicone gasket maker around the air filter gasket (on the filters’ metal screen side or cover side). Let it cure until it is firm and reinstall air filter. After you mow for awhile check the carburetor inlet again as above. It should be clean and you should see a grooved impression all around the sealer you applied where the cover is now sealing against it. You’ll see it dirty outside the groove and clean inside the groove and consistent all the way around. Success! Peace…

  2. Mary says:

    My mower will start and run with the air filter off, but as soon as you put it back on, it won’t do either. Any suggestions??

    • Hi Mary!

      First thing, be sure you NEVER run your mower without the air filter on, it can easily suck debris in and severely damage your engine.

      But to fix your problem, try getting a new filter, if your current one is dirty or damaged it could be the problem.

      If that doesn’t work, install your air filter and look all around it, being sure to take notice if there are any holes or spaces where air could be getting through.

      If your air filter is connected to a tube and there is a gasket anywhere, check the gasket, and replace it, if any air is slipping in or out while your air filter is connected it could be what is causing your problem.

      Best of luck and I hope you get it figured out soon!

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