Dealing with a Stihl MS 250 that refuses to start or perform as it should can be a frustrating experience for any homeowner or professional landscaper. This reliable chainsaw model is a popular choice for managing medium-duty cutting tasks, yet even the most robust tools require attention and maintenance over time. Understanding the fundamental principles of operation and common points of failure is the first step toward resolving issues quickly and effectively.
Common Symptoms Indicating Trouble
Before diving into complex repairs, it is essential to identify the specific symptoms your Stihl MS 250 is exhibiting. A chain that spins intermittently or not at all points to issues within the ignition or clutch systems. Alternatively, if the engine fires up but dies immediately when the throttle is engaged, the problem likely resides in the fuel delivery or air filtration pathways. Paying close attention to these signs allows for a targeted approach rather than a trial-and-error dismantling of the machine.
Fuel System Verification and Maintenance
The majority of starting and running issues with the MS 250 stem from the fuel system. Stihl requires a specific mixture of high-quality gasoline and two-stroke oil to function correctly; using the wrong ratio or stale fuel is a primary cause of poor performance. Clogged fuel filters or a blocked fuel line prevent the necessary pressure from reaching the carburetor, starving the engine of the combustible mixture it needs to run smoothly.
Steps to Check the Fuel Delivery
Inspect the fuel tank cap’s vent hole for blockages, as a vacuum can form preventing fuel flow.
Examine the fuel filter located at the end of the tank pickup tube for debris or discoloration.
Check the fuel lines for cracks, kinks, or brittleness that might restrict the fuel supply.
Air Filter and Carburetor Inspection
A dirty air filter restricts airflow, causing the fuel mixture to run too rich, which results in loss of power and difficult starting. The carburetor, the device responsible for mixing air and fuel, is sensitive to vibrations and impurities in the fuel. Over time, the jets within the carburetor can become clogged with varnish or debris, disrupting the precise air-to-fuel ratio required for optimal combustion.
Addressing Carburetor Issues
While cleaning a carburetor on a Stihl MS 250 is possible for experienced users, it often requires specific tools and a delicate touch. If the chainsaw starts but runs poorly, a professional-grade carburetor cleaning kit can help dislodge deposits. However, if the unit is damaged or the diaphragms are worn, replacement is often the most efficient solution to restore peak performance.
Spark Plug and Ignition Checks
The spark plug is the literal spark of life for the engine, and its condition provides valuable insight into the health of the machine. A fouled or gap-incorrect plug will cause misfires or prevent the engine from starting altogether. Regular inspection and replacement of this component are simple yet critical maintenance steps that prevent more significant mechanical failures.
Spark Plug Maintenance Procedure
Disconnect the spark plug wire and remove the plug using a socket wrench.
Examine the electrode for heavy carbon buildup or damage.
Check the gap with a feeler gauge and adjust or replace the plug to match the specifications outlined in the owner’s manual.
Chain and Bar Assessment
Mechanical issues are not always related to the engine’s internal workings; sometimes the problem is external. A stretched chain or a warped bar creates excessive drag, causing the engine to stall under load. Ensuring the chain tension is correct and the bar is lubricated properly reduces stress on the motor and ensures efficient cutting performance.
