Air Filter Cleaning – Replacement Guide for 1991 Suzuki RM125

Shop parts for a 1991 Suzuki RM125 Dirt Bike.

Maintaining the air filter is essential for the reliability & power of your 1991 Suzuki RM125. This guide by MotoSport.com offers a step-by-step proprietary process to help you keep your bike performing at its peak on every ride—whether you're racing or trail riding.

Model-Specific Notes

  • The 1991 RM125 uses a foam air filter element, which is designed to be repeatedly cleaned and oiled for protection in harsh off-road environments.
  • The air filter location allows easy access but is prone to trapping sand and fine dust, especially in dry conditions. Regular checks and cleaning will prevent engine wear or damage.
  • This model's motocross heritage means optimal airflow is critical—never skip maintenance or use incorrect filter oil.

Required Tools & Materials

  • 8mm or 10mm wrench
  • Non-flammable cleaning solvent (e.g., specific foam filter cleaner)
  • Foam filter oil
  • Disposable gloves
  • Clean rags or paper towels
  • Plastic bags

Step-by-Step Air Filter Removal

  1. Remove the seat by undoing the rear mounting bolts.
    This exposes the airbox.
  2. Take off the air cleaner box lid.
  3. Unscrew the wing nut holding the filter in place.
  4. Lift out the foam filter element. Inspect its surface for heavy dirt or signs of damage. Replace if the foam is torn or severely worn.

Cleaning Procedure

  1. Fill a wash pan with non-flammable cleaning solvent.
  2. Completely immerse the foam filter.
  3. Squeeze the filter gently to work out dirt & old oil. Do not wring or twist; this causes the foam to crack & degrade.
  4. Rinse until all dirt is removed. Repeat if necessary.
  5. Place the filter in a clean plastic bag to dry thoroughly.

Oiling & Reinstallation

  1. Pour foam filter oil evenly over the dry filter inside a clean bag.
  2. Knead the filter to distribute oil evenly into all pores.
  3. Squeeze out excess oil gently—avoid dripping but ensure full coverage.
    A lightly oiled filter captures dust best. Too much oil restricts airflow; too little leaves the engine vulnerable.
  4. Inspect the air box rim and clean off any residual dirt with a rag.
  5. Apply a thin layer of waterproof grease to the rim of the air filter for a perfect seal, preventing unfiltered air from bypassing around the edge.
  6. Install the filter back onto its holder, secure with the wing nut, and refit the air box lid and seat.

Proprietary MotoSport Tips

  • Check the air filter every ride in sandy or dusty environments common to the RM125. Cleaning more often than usual is recommended.
  • Consider an outerwear pre-filter kit if riding in deep sand—this adds a first layer of defense and lessens cleaning intervals.
  • Always use dedicated foam filter oil; automotive engine oil lacks the required stickiness and filtration properties.
  • If replacing the filter, ensure fitment matches the unique cage & airbox design of the 1991 RM125.

Expert Advisory for Your 1991 RM125

  • If you notice power loss, difficulty starting, or increased engine noise, inspect the air filter immediately. Severe filter neglect can lead to costly engine damage on this model.
  • Keep the filter sealing surface spotless and check for cracks or deformities in the filter cage, as leaks can occur over time.

The 1991 Suzuki RM125's air filter is a critical line of defense for your engine—routine cleaning and periodic replacement help maintain legendary two-stroke power and reliability. Ride harder and longer with MotoSport's proprietary care guide.

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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.