How to Troubleshoot the STIHL MS 250 Chainsaw

Written by ross glyn
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How to Troubleshoot the STIHL MS 250 Chainsaw
Keep your garden clear with a STIHL MS 250 Chainsaw. (chainsaw image by Andris Daugovich from

The STIHL MS 250 is a lightweight and powerful chainsaw. However, as with most cutting tools, wear and tear inevitably occurs. The problems are relatively simple to troubleshoot, whether it is an issue with the chain's tension, spark plug, or an engine that is idling rough. Run through a few troubleshooting steps before taking your chainsaw in for service.

Skill level:
Moderately Easy

Things you need

  • spark plug wrench
  • spark plug gap tool

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  1. 1

    Check the spark plug if the engine is low on power, difficult to start or runs poorly at idling speed. Pull off the rubber spark plug boot. Use the spark plug wrench to unscrew the plug. Dry the spark plug. Replace the plug if it is corroded. Crank the engine a few times to clear the combustion chamber. Check the electrode gap on the end of the plug and use the spark plug gap tool to adjust, if necessary. Refit the spark plug and boot.

  2. 2

    Adjust the speed screws if the chain runs while the engine is idling. Slowly screw the low-speed screw "L" clockwise down to its seat. Turn the screw one full turn counterclockwise from that position. Turn the idle speed screw "LA" slowly counterclockwise until the chain stops running. Turn the screw another quarter of a turn in the same direction.

  3. 3

    Adjust the low-speed screw "L" if the engine idles erratically or has poor acceleration. The idle setting is too lean. Turn the low-speed screw counterclockwise until the engine runs and accelerates smoothly. It is usually necessary to adjust the setting of the idle speed screw "L" as well after each correction to the low-speed screw.

  4. 4

    Tension the saw chain if it is not spinning on the guide bar correctly. Shut off the engine. Pull out the hinged clip and loosen the wing nut that holds the guide blade and saw chain to the unit. Turn the adjusting wheel (on top of the unit) clockwise until it stops. Tighten the wing nut by hand until secure. Fold down the wing nut's hinged clip. There should be no gap between the chain and the guide bar. The guide bar is the flat metal bar that the chain surrounds.

Tips and warnings

  • Fit a new spark plug after approximately 100 hours of operation.
  • Always wear protective eyewear when using the chainsaw.
  • Always move the master control to the stop position and engage the chain brake to prevent the engine starting unintentionally.
  • Always check to see that the spark plug boot is secure. A loose boot may cause arcing that could ignite combustible fumes and cause a fire.
  • Always start the chainsaw on level ground.
  • Always operate the unit with both hands firmly on the handles.

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