Foam Air Filter The Green Layer Does the Lifting

Two layers of foam, each handling a slice of the dust. The CR125 air filter element is exactly that two-layer build.

The layer the air meets first is the green one. Green is not decoration; it means the foam is oiled. The oil film traps the coarse grit, grass and insects, and that is the first sieve. This foam's cells are coarse, so the engine gets its air, and the rough stuff stays out.

Why a second layer at all? The coarse layer stops the big pieces, but fine dust rides in with the air. The white inner foam's cells are finer, and it catches that fine dust, so the engine breathes clean air. One coarse, one fine, each taking its slice; the pair filters cleaner than a single layer, and breathes better than a paper element.

Why is it a bowl, with a ring in the center? The element seats into the air cleaner box, and the bowl shape wraps the box's cavity, the air coming in from the sides and toward the center. The black rubber ring in the center is the intake grommet, lining up with the carburetor's intake passage, the ring hugging the edge so the air passes through the ring and does not leak around it.

Can the foam be washed? Yes. Take it off, and wash it with a dedicated cleaner or clean water, never gasoline, which eats the oil film in the foam. Squeeze it gently, let it dry, thin it with a coat of air filter oil, and refit it. A clean wash means it keeps working.

When to replace it? The foam hardens, crumbles, will not wash clean, or tears open and will not hold even after washing, then swap it. Foam ages, and a clean wash does not make it last forever.

What to check when fitting it? Line up the bowl's curve and the position of the center grommet on the new element against the old one. Underbone bikes of the same type mostly fit, but fit is not guaranteed for every one, so comparing against the old part is the safe way. Press it flat into the box, center the grommet on the intake passage, snap the box lid on, and only start once the air path is tight.