The air filter is your engine's first line of defense against dirt and debris. A clogged filter starves the engine of air, causing it to run rich, lose power, and waste fuel. A damaged or missing filter allows dirt directly into the cylinder, scoring the walls and destroying the rings. Checking and replacing the air filter is one of the easiest maintenance tasks you can do.
How Often Should You Check the Air Filter?
- Every 25 hours of operation (about once a month for regular use)
- Before each season of use
- After operating in dusty conditions (more frequently)
A filter that looks clean to the eye can still be restrictive. Hold it up to the sun or a bright light — if you can't see light through the paper, it needs cleaning or replacement.
Types of Air Filters
1. Paper Element Filters
Most common on push mowers, riding mowers, and pressure washers. They're disposable — you clean them by tapping, but eventually replace them.
2. Foam Filters
Common on older equipment and some handheld tools. Foam filters can be washed, oiled, and reused.
3. Dual-Element Filters (Foam Pre-Filter + Paper Main Filter)
Common on riding mowers and generators. The foam pre-filter catches large particles; the paper filter handles fine dust. You clean the foam and replace the paper.
Step-by-Step: Inspecting and Replacing
Step 1: Locate and Remove the Filter
The air filter housing is usually a plastic or metal box on the side of the engine, connected to the carburetor. Remove the cover — most have a wing nut, clips, or screws. Lift out the filter element(s).
Step 2: Inspect the Filter
Paper filter: Tap it gently on a flat surface to dislodge loose dirt. If it's dark, oily, or you can't see light through it, replace it. Never wash a paper filter with water — it destroys the filtering media.
Foam filter: Inspect for tears or brittleness. If it's intact, it can be cleaned and re-oiled. If it's crumbling or torn, replace it.
Step 3: Clean or Replace
Paper filter (reusable for now): Tap gently to remove loose dirt. Use compressed air from the inside out if available. If it's still dirty or damaged, replace it.
Foam filter (reusable): Wash in warm soapy water, rinse thoroughly, and let it dry completely. Saturate it with air filter oil (available at any auto parts store), then squeeze out the excess — do not wring or twist. The filter should be damp, not dripping.
Step 4: Clean the Housing
Wipe out the air filter housing and the sealing surface with a damp rag. Dirt in the housing will be sucked into the engine when you reinstall the filter. Check the sealing gasket on the cover — if it's cracked or missing, replace it to prevent unfiltered air from entering.
Step 5: Reinstall
Install the filter in the correct orientation. Most paper filters have a specific direction (the sealed edge faces out). Reinstall the cover and tighten the wing nut or clips snugly.
Signs You Need to Replace the Air Filter
- The engine runs rough or stalls
- Black smoke from the exhaust (rich mixture)
- Reduced power under load
- The engine won't start or starts hard
- The filter is visibly damaged, oily, or has holes
A Quick Test
If your engine is running rough and you suspect the air filter, remove it and run the engine for a minute. If the engine runs better without the filter, the filter was the problem. Don't run the engine longer than this test — unfiltered air will damage the engine.
The Bottom Line
Air filters cost $5–15 and take 5 minutes to replace. A clogged filter costs you fuel economy and power. A missing or damaged filter costs you an engine. Check it every 25 hours and replace it every season at minimum.