The air filter on a lawn mower keeps impurities in the air from making it into the engine, thus resulting in better performance and more power. Over time the air filter can get worn and dirty. Replacing the air filter is an easy process, and it can keep your mower running at peak performance. A new air filter (part #491588s) can be purchased for about $5 or $6 -- Amazon.com currently lists it for $5.93. ($5.50 as of 3/29/15.)
The steps below will guide you through replacing the air filter on a Craftsman model 917.376741 or similar 22" push lawn mower. All you'll need are a flathead screwdriver, the new air filter, and some rags or paper towels.
1. Remove the air filter cover
The air filter is located on the same side of the mower as the gas tank, and it sits behind a protective cover. The cover is on the side of the mower, below the gas cap and toward the front of the mower.
One screw holds the cover in place -- you can loosen this screw with a flathead screwdriver. The screw won't come all the way out, but once it's loose enough you can pull the air filter cover off.
2. Remove the air filter
The air filter fits into the cover, and can be removed by pulling it straight out. While you have the air filter removed, now is a good time to wipe down the inside of the cover, as well as the exposed part of the mower, with a paper towel or dry rag.
3. Install the new air filter
Place the new air filter onto the cover, so that the flat side faces away from the cover (toward the engine). The air filter should fit into the cover snugly.
4. Reattach the cover
With the air filter still fitted into the cover, reattach the cover onto the mower. Line the screw up with the screw hole and tighten the screw so that the cover is held in place.
(originally published on Helium.com, Sept 2011)