Air Filter Cleaning – Replacement Guide for 1991 Yamaha PW50

Shop parts for a 1991 Yamaha PW50 Dirt Bike.

The 1991 Yamaha PW50 is a legendary starter dirt bike designed for young riders. To ensure the two-stroke engine operates smoothly and maintains longevity, it is crucial to keep the air filter in top condition. Below is MotoSport.com's exclusive, model-specific guide to cleaning and replacing the air filter on your PW50, along with unique tips for this model year.

Understanding the PW50 Air Filter

The PW50 uses a foam air filter element housed in a dedicated airbox. The OEM design is simple to remove, clean, and reinstall. It is a dual stage filter, meaning it uses both a coarse outer foam to catch larger debris and a fine inner foam for finer dust, providing superior filtration and airflow essential for the PW50's small but mighty engine.

How Often Should You Service the Air Filter?

  • Clean the air filter every 3–5 rides, more often if riding in extremely dusty conditions.
  • Replace the filter if it is torn, misshapen, or doesn't seal properly in the airbox.

Cleaning the 1991 Yamaha PW50 Air Filter

  1. Remove the seat and filter cover – Release the seat latch and unscrew the air filter cover on the left side of the bike.
  2. Take out the foam filter – Gently pull out the foam filter element from the airbox.
  3. Inspect the filter – Look for tears, hardened foam, or excessive wear. If damaged, replace with a new filter element.
  4. Pre-clean – Carefully tap the filter to knock off loose dirt.
  5. Wash the filter – Submerge the foam in a tub of warm water and mild detergent or a dedicated foam filter cleaner. Squeeze gently (do not wring) to remove contaminants. Rinse thoroughly until water is clear.
  6. Dry completely – Allow to air dry fully, as using heat can damage the foam's structure.
  7. Apply filter oil – Once dry, pour special foam filter oil onto the filter, working it through so the entire filterincluding seams and cornersis evenly coated. Squeeze out any excess oil.
  8. Reinstall – Replace the filter in the airbox, ensuring the sealing edge contacts the airbox surface uniformly. Secure the cover and seat.

Replacing the Air Filter (if necessary)

  • Use a replacement foam filter specifically designed for the PW50. A dual stage filter (coarse outer + fine inner) provides best results and durability.
  • Before installing, oil the new filter as described above.
  • Check that the filter fits tightly, as a loose fit can allow dirt into the engine.

PW50 Model-Specific Notes

  • The PW50's compact airbox can sometimes retain moisture or dirt at the base. Always wipe clean before reinstalling the filter.
  • OEM replacement filters for 1991–2021 models use nearly identical dimensions, making installation straightforward. Fitment is universal across the entire PW50 model line from 1981 onwards.
  • Since the PW50 is often ridden by young or beginner riders, be sure to inspect the entire air intake area for signs of over-oiling, which can restrain airflow and foul the spark plug.

Pro Tips for Owners

  • Always keep a spare filter on hand—swap in a clean one while the other is drying.
  • Use only cleaners and oils intended for foam filters to avoid damaging filter materials.
  • Regular filter maintenance not only protects your motor but also maximizes throttle response and power on the track or trail.

With this MotoSport air filter care guide, your 1991 Yamaha PW50 will be ready for every ride, keeping that peppy little engine protected and performing its best.

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Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.