how do i clean the air filter on my stihl ms 250? it's absolutely caked in sawdust

Diagnosis

When your STIHL MS 250 air filter is "caked," the engine is effectively suffocating. The MS 250 uses a high-density foam or pleated material designed to trap fine particulates before they reach the cylinder. When sawdust mixes with bar and chain oil, it creates a sticky, impermeable paste that seals the pores of the filter. This restricts airflow, causing the engine to run "rich" (too much fuel, not enough air), which leads to carbon buildup on the piston and a noticeable loss of RPMs during cutting.

You can confirm the filter is the culprit if the saw starts easily but "bogs down" or dies when you apply pressure to the wood, or if you notice a dark, sooty residue on the spark arrester screen of the muffler. If you remove the filter and the saw suddenly screams with more power, your filter was completely obstructed. Failure to clean this regularly will lead to overheating and potential seizure of the engine due to improper fuel-to-air ratios.

How to Fix It

Follow these precise steps to restore airflow to your MS 250:

1. Turn the saw upside down on a clean workbench to prevent sawdust from falling into the carburetor intake once the filter is removed.
2. Rotate the filter cover locking knob (located on the side of the housing) counter-clockwise to unlock it. Pull the cover straight back to expose the filter element.
3. Carefully lift the filter element out of the housing. If you have the pleated version, avoid poking holes in the fabric; if you have the foam version, do not tear the edges.
4. Tap the filter firmly against a hard surface to knock loose the heavy "cakes" of sawdust.
5. Submerge the filter in a basin of warm water mixed with a mild dish soap (like Dawn). Avoid using gasoline, kerosene, or harsh industrial degreasers, as these break down the cellular structure of the foam and create microscopic holes that allow dirt into the cylinder.
6. Squeeze the filter gently—do not wring or twist it, as this will deform the shape and create gaps around the seal. Rinse under clean running water until no more soap bubbles appear.
7. Pat the filter dry with a clean cloth and let it air dry completely. Installing a damp filter can suck water droplets directly into the carburetor, causing the saw to stall.
8. While the filter is out, use a can of compressed air or a soft brush to clean the interior of the air intake area and the cooling fins on the flywheel housing.
9. Slide the dry filter back into place, ensuring it seats flush against the carburetor intake, and lock the cover back into position.

If That Didn't Work

• Replace the Filter Element: If the foam has become "spongy" or the pleated fabric has developed pinholes, cleaning will not work. Replace it with a genuine STIHL replacement filter (Part # 114.2186.000) to ensure a perfect airtight seal.
• Clean the Spark Arrester: If the engine still feels sluggish, the exhaust is likely clogged. Remove the muffler and unscrew the small wire spark arrester screen. Use a torch to burn off carbon deposits or clean it with a wire brush.
• Check the Carburetor Adjustment: If the filter is clean but the saw still bogs, the "H" (High) or "L" (Low) adjustment screws may have drifted. Use a combination tool to slightly lean out the mixture to compensate for the new airflow.
• Inspect the Fuel Filter: A clogged fuel filter in the gas tank can mimic the symptoms of a dirty air filter. Use a fish-hook tool to pull the fuel filter out of the tank and replace it if it appears dark brown or slimy.

Heads Up

• Refuel Rule: Make it a habit to tap out the air filter every single time you refill the gas tank; this prevents the "caking" from becoming permanent.
• Avoid Compressed Air: Never blow high-pressure air through a foam filter from the inside out, as this pushes dirt deeper into the pores and can create invisible tears in the material.
• Oil Warning: If you notice the filter is saturated in oil, check your spark plug. Excessive oil in the filter often indicates a leaking carburetor or a faulty fuel pump.
• Seasonal Storage: If storing the saw for winter, remove the filter and inspect it. A damp filter left in storage can grow mold, which will restrict airflow when you restart the saw in the spring.