The air filter is a very important part of the engine. It allows fresh air to enter and mix with the gasoline, but at the same time it keeps dust and debris out. The air filter should be inspected, cleaned, and replaced regularly.
There are several different kinds of air filters. Two popular kinds used on lawn mowers include a foam air filter (typically soaked in oil) and a paper air filter. The paper air filter looks like the air filter you might find in a vacuum. Some paper air filters will be enclosed inside a foam pre-cleaner. This pre-cleaner can be cleaned, and it will prolong the life of the air filter, but it will also need to be replaced eventually.
The air filter is probably located on the same side of the engine as the fuel tank and the carburetor. Removal instructions will vary by lawn mower model, and they should be printed in either the operation manual or the engine manual, but typically all you'll need to do is remove a plastic cover that's probably held down by one screw (either on the top of the engine or on the side) and then remove the air filter and either clean it or replace it with a new one. When installing a new air filter, be sure to install it in the same orientation as the old filter.
Here are some links to air filter replacement instructions for specific mower models.
- Bolens 22" Push Mower
- Craftsman Power Propelled 22" Rotary Lawn Mower (model 917.376741 or similar)
- Honda HRX217VKA / HRX217HYA / HRX217HZA 21" Versamow Mower
- Husqvarna HU700F 22" Self-Propelled Lawn Mower
- Lawn-Boy 10640 / 10641 / 10642 / 10645 / 10646 / 10647 20" Push Mower
- Toro 20331 22" High Wheel Recycler Mower
- Toro 20332 22" Personal Pace Recycler Mower
- Toro 20339 / 20339C 22" Recycler Lawn Mower with SmartStow
- Toro 20350 22" Low Wheel Recycler Self-Propelled Mower
- Troy-Bilt TB210 / TB230 / TB280Es 21" Self-Propelled Mower
- Yard Machines 21" High Wheel Push Mower
- Yard-Man 11B-106C401 / 11B-106C701 20" Mulching Push Mower