Air Filter Box Yamaha BW's / Slider before 2004

Air filter box

Most vehicles with an internal combustion engine have an air filter box, or airbox. The reason for this is that an engine needs air to function, and this air must be clean to allow for reliable engine performance. This means the air has to be filtered, and the filter also needs to stay dry in order to filter efficiently.
The air filter box houses this filter and protects it from getting wet and dirty.

Air filter box: performance

The size of the air filter box varies from vehicle to vehicle. The air volume affects engine performance.
Powerful engines (racing cylinders) or engines with large displacement (big bore) often require a larger air volume. For this reason, tuned two-wheelers sometimes do without the original airbox and instead install an open pod air filter, or opt for a larger air filter box, such as a karting airbox, toto continue to protect the filter effectively.

Unlike in scooters and mopeds, the original air filter box of motocross motorcycles is usually sufficient even if the engine is heavily tuned.