Air Filter Cleaning – Replacement Guide for 1978 Honda CR250

Shop parts for a 1978 Honda CR250 Dirt Bike.

The legendary 1978 Honda CR250 is respected for its lightweight frame, aggressive powerband, and pivotal role in motocross history. To keep your vintage machine performing at its best, routine air filter maintenance is critical. Clean air means a healthy engine—especially for a two-stroke like the CR250 where dirt ingestion can result in catastrophic engine damage or top-end wear.

What Makes the 1978 CR250 Unique?

This model uses a dual-stage foam air filter inside the stock airbox. The OEM part number is 17213-430-000. These filters are designed to maximize air flow and trap dirt in two distinct layers: a large-pore pre-filter for heavier debris and a fine-pore inner layer for dust and minute particles. A proper seal at the mating surface is ensured by an integrated grease groove that keeps unfiltered air out and performance up.

How Often Should You Service the Air Filter?

Ride frequency and environment determine maintenance intervals, but for best results, inspect after every ride. If you're riding in dusty or sandy conditions, clean or replace the filter after every ride. At minimum, clean the filter every 10 hours of use or after particularly dirty rides.

Required Tools & Supplies

  • Rubber gloves
  • Uni or dual-stage foam filter (OEM or aftermarket equivalent)
  • Foam filter cleaner or mild biodegradable degreaser
  • Filter oil (specific for foam filters, do not use motor oil)
  • Clean rags
  • High-tack filter grease
  • Bucket or wash basin
  • Air box sealing grease (optional, recommended for older bikes)

Step-by-Step Cleaning Instructions

  1. Remove the seat by loosening the seat bolts and carefully set aside.
  2. Remove the air filter cover (if equipped) and carefully pull the filter from the airbox. Take caution not to drop dirt or debris into the intake tract.
  3. Inspect the filter and cage for rips, tears or structural problems; replace if damaged.
  4. Tap the filter gently to knock off loose dirt.
  5. Fill a bucket with warm water and foam filter cleaner (or a mild degreaser). Submerge and gently knead the filter until contaminants are removed. Avoid wringing or twisting, which can rip seams or foam.
  6. Rinse completely with clean water. Repeat the cleaning until all oil and dirt are gone. Squeeze out excess water gently.
  7. Allow the filter to dry completely—some owners use a fan to speed the process.
  8. Once dry, pour foam filter oil evenly over the filter and work it through until uniformly coated. Pay extra attention to the sealing edge.
  9. Apply a thin bead of filter grease to the filter's sealing surface for maximum dirt protection.
  10. Inspect the airbox and filter cage for dust, dirt, or water; wipe clean as needed.
  11. Reinstall the filter onto the cage and seat it properly in the airbox, ensuring a tight fit and continuous seal all around. Replace the filter cover and the seat.

Replacement Tips and Best Practices

  • If your filter is saturated with dirt or the foam is crumbling, replace with a new dual-stage foam filter for the 1978-1980 CR250. Periodically check the cage and intake for signs of deterioration or cracking—these parts are now over 40 years old.
  • Always keep a spare pre-oiled filter on hand for racing or consecutive ride days.
  • When riding in particularly dusty trails, using a disposable filter skin can help extend cleaning intervals and protect your stock filter.

Important Notes for 1978 CR250 Owners

  • Always use a dual-stage foam filter for maximum protection. Universal or paper element filters may not provide adequate dirt-trapping ability for vintage two-strokes.
  • Inspect the airbox boot and intake tract regularly for cracks and air leaks – air leaks can cause poor running or even engine failure.
  • Pay attention to the Ultra Seal grease groove on modern replacement filters; grease it fully before installation for the best sealing effect.
  • Monitor filter fitment. Manufacturing differences in aftermarket filters may affect how well they seal in the old OEM airbox – always double-check before you ride.

Regular, careful air filter maintenance is the key to preserving your 1978 Honda CR250’s legendary performance and reliability for years to come. Keep it clean, keep it sealed, and ride on.

Related Shopping Categories

Shop Air Filters for a 1978 Honda CR250 Dirt Bike.

Shop Air Filter Oil for a 1978 Honda CR250 Dirt Bike.

Shop Air Box Covers for a 1978 Honda CR250 Dirt Bike.

Shop Tools for a 1978 Honda CR250 Dirt Bike.

Shop Intake Parts for a 1978 Honda CR250 Dirt Bike.

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.