Air Filter

The air filter cleans the air before it enters the engine. Even fine dust acts like grinding paste on cylinders, piston rings and valves, so a damaged or badly fitted filter can wear out an engine surprisingly quickly.

• Paper filters are common on road bikes and are replaced, not cleaned.
• Oiled foam filters are standard on motocross, enduro and ATVs; they are washed and re-oiled.
• Oiled cotton gauze filters are washable and often sold as performance upgrades.

Follow the service interval, but check more often in dusty or wet conditions; off-road bikes may need a clean after every ride. A clogged filter makes the mixture rich and reduces power. Make sure the filter seals all round the airbox.