Air Filter for Stihl FS 38 / FS 45 / FS 55 (4140 124 2800)

What it is

This is a pattern (non-Stihl) replacement air filter listed as equivalent to Stihl part 4140 124 2800, for the FS 38, FS 45, FS 55, KM 55 and HL 45. Despite the generic name it has carried on our site, it is model-specific: if your machine isn’t on that list, match the shape and part number of your old filter instead.

Why the air filter matters

The filter sits between the outside air and the carburettor. A brush cutter works in a constant haze of grass dust and grit right next to its air intake, so the filter clogs faster than on most small engines. A blocked filter starves the engine — hard starting, hesitation, poor power — and a torn one lets dust through to the piston and cylinder, which is far more expensive to fix than a new filter.

How to look after it

Check the filter every few hours of use and tap or brush it clean; how to clean and dry it properly is covered in how to clean a brush cutter air filter. Replace it when it’s torn, hardened, oil-soaked or still discoloured after cleaning. Never run the engine without a filter, even for a minute.

Honest limitations

Pattern parts can differ slightly from genuine ones in fit and filtering, so compare it with the old filter before fitting. A new filter won’t cure an engine that’s already running badly for other reasons — check the spark plug and fuel filter too (see brush cutter maintenance). When we checked in October 2026, the Amazon.co.uk listing couldn’t be dispatched to our location, so check availability before relying on it.