KL125 Air Filter Yellow Filters Black Seals

On the KL125 air filter, the yellow does the work and the black does the sealing.

This is the round bowl sponge element for a dirt bike: a yellow bowl of foam, with a black ring at the top and a black ring at the bottom.

Why two colors? The yellow bowl is the part that filters. Air from the box has to pass through the yellow foam on its way to the engine, and the fine dust is caught in the sponge. The black rings are the part that seals, one at the top and one at the bottom, pressing the element down into the groove of the airbox so that no air slips past the filter and reaches the cylinder. Without that seal, the filtering is for nothing.

Why a bowl? This kind of round element sits in a round bowl box, and the bowl shape follows the wall of the box, so there is no gap at the edge. Air comes in along the inside of the bowl, goes through the sponge wall, and on to the cylinder. The path is short and the resistance is low, which is what a dirt bike wants when it is being revved hard.

Can it be washed? A sponge element can be washed. Use a mild detergent, work the dust out under the water, squeeze it dry, soak it in air filter oil, or engine oil if you do not have any, and squeeze again until the oil is spread through the whole element. Give it time to set, then refit it. A washed element is not a new one; when the sponge has torn, a ring has gone out of shape, or the black ring is crumbling, it is time for a new element.

How do you know it is time? Holes in the sponge wall, rings that no longer seat, an intake that sounds noticeably hollow, or oil being pulled past. A few washes and it still will not hold, and it is done.

Does it fit other machines? The same family of dirt bike numbers, KX250, KLX250 and KX500, run elements of this shape. Fitment is not guaranteed, so measure the diameter of the old element, the width of the rings and the depth of the bowl, and match them before you order.