Unlike the dry paper air filter cartridges used in most passenger vehicles, Yamaha race motorcycles -- the YZ250 in particular -- uses a wet-type air filter element. This type of air filter is made from foam and is saturated in oil. This allows the element to pick up the tiniest of dirt particles, which is ideal for the dusty conditions that this type of cycle is used in. The air filter of your YZ250 requires frequent cleanings, which involves removing the element from the cycle.
Things You'll Need
- 10-mm socket
- 8-mm wrench
- Small container
- Air filter cleaning solvent
- Foam air filter oil
- Lithium grease
- Torque wrench
Remove the retaining bolt on the plastic number plate near the backside of each side of the seat with a 10-mm socket and ratchet. Pull straight up on the back of the seat, then slide it towards the rear of the cycle. Remove the seat from the bike to expose the air box underneath.
Remove the bolt and washer on the end of the air filter assembly with an 8-mm wrench. Pull the air filter straight up and out of the air box.
Slip the foam filter element off the plastic filter guide. Inspect the foam element for damage. Replace the element, if it is torn or has any holes in it.
Submerse the foam filter into a container half-filled with filter cleaning solvent. Gently knead the filter with your fingers to remove dirt from the filter.
Remove the foam filter element from the solvent. Squeeze the excess solvent -- do not wring it -- from the element. Squeeze as much solvent out of the element as you can, or the engine may be hard to start once the element is installed.
Spray foam air filter oil onto the element. Squeeze out any excess fluid from the filter. Note that the element should be completely saturated with oil, but not to the point that is dripping from the element.
Slip the foam element back over the plastic filter guide. Slide the hole in the element over the pin that protrudes from the guide. Apply a thin coating of lithium grease to the mating surface of the element where it makes contact with the intake port in the air box, as this will make an air-tight seal between the element and the intake.
Position the filter assembly into the air box so that the pin protruding from the filter guide is inserted into the corresponding hole in the air box. Replace the washer and the retaining bolt through the hole in the center of the element and guide. Tighten the bolt finger tight, then tighten it with a torque wrench to 1.4 foot-pounds.
Slide the seat into position and tighten the retaining bolts finger-tight. Tighten the bolts to 17 foot-pounds with a torque wrench.
Tips & Warnings
- Clean and lubricate the air filter after initial engine break-in and before every race.
- According to Yamaha, never run the engine of your YZ250 without the air filter installed. Failure to do so may allow dirt to engine the engine, which could cause the internal parts to wear rapidly.
- MX Guy: 2003 YZ250F Service Manual
- “Yamaha YZ250F 2001-2003 Repair and Maintenance Manual“; Clymer