STIHL MS 250 Service Manual

Section about safety and overview

The STIHL MS 250 chainsaw is a compact power tool designed for light to medium logging, pruning, and firewood preparation. Its operation requires careful attention to safety procedures and proper personal protective equipment (PPE) to reduce the risk of injury. Before each use, inspect the saw for damaged parts, loose fasteners, and signs of wear on the bar and chain. Verify that the chain brake, throttle lock, and stop switch function correctly, and ensure the chain is properly tensioned and lubricated. A thorough safety mindset and routine checks are essential to prevent kickback, contact injuries, and fuel-related hazards.

Personal protective equipment is a critical component of safe operation. At a minimum, wear cut-resistant gloves, sturdy boots with good traction, and eye and ear protection. A helmet with a face shield can protect against flying debris, while hearing protection mitigates noise exposure during extended use. Always use chainsaw chaps or cut-resistant pants and a long-sleeved shirt to shield exposed skin. When refueling or performing maintenance, gloves and eye protection are especially important to prevent contact with fuel and lubricants. Establish a clear work area free of bystanders and obstacles, and maintain a secure stance with both hands firmly on the saw during operation.

Overview of STIHL MS 250 chainsaw features includes a lightweight design that balances portability with performance. The engine delivers reliable mid-range torque suitable for versatile cutting tasks, while the bar length is typically chosen to match the job at hand. The air filtration system helps protect the engine from dust and debris, extending service life in dirty or dusty environments. The automatic oiler keeps the chain lubricated to reduce heat build-up and wear, though users should periodically check oil levels and adjust flow as needed for different cutting conditions. A well-designed anti-vibration system reduces operator fatigue, enabling longer periods of productive use with increased control and comfort.

Ease of maintenance is another hallmark of the MS 250, with accessible access to the air filter, spark plug, and fuel system components. When performing routine maintenance, follow the manufacturer’s recommended intervals and use approved STIHL parts and lubricants. Replace the spark plug if the engine is hard to start or runs unevenly, and check the fuel mixture to ensure correct octane and oil ratio for two-stroke operation. Proper chain sharpening and tensioning, along with bar inspection for wear or burrs, help maintain cutting efficiency and safety. In every maintenance scenario, work with the engine off, the bar away from your body, and the chain brake engaged to minimize risk during service procedures.

The STIHL MS 250 is a mid-range chainsaw designed for versatile cutting tasks, from firewood preparation to light felling. Operating the engine safely begins with a clear understanding of the shutdown and start procedures, ensuring that you can start the saw reliably in various conditions. Before the first start, inspect the air filter, spark plug, and fuel system for signs of wear or damage, and confirm that the chain brake is engaged to prevent accidental motion. When starting the engine, place the saw on a stable surface, engage the rear handle with a firm grip, and ensure the chain is disengaged from the guide bar. Always perform a cold-start procedure following the manufacturer’s guidelines, and never attempt to start the engine with the saw in gear or with the chain touching the ground. After starting, allow the engine to reach its normal operating temperature before applying full throttle, which helps extend engine life and improves cutting performance over time.

The throttle and choke combination on the MS 250 is designed to provide smooth operation across a range of temperatures and workloads. The choke should be used when starting a cold engine and gradually opened as the engine warms, ensuring stable idle and preventing lean running conditions. The throttle lever controls the engine speed and should be modulated carefully during cutting to maintain consistent chain momentum without overloading the engine. When performing routine maintenance or cleaning, use the throttle to hold the engine at a low, steady RPM to facilitate safe access to components. Always return the choke to the open position and verify that the throttle spring returns to a neutral state when releasing the trigger. This prevents unintended throttle engagement and contributes to safer operation in dynamic cutting environments.

Lever and switch functions on the STIHL MS 250 are designed to provide clear, intuitive control over safety, starting, and operation. The chain brake must be activated via the front hand guard before beginning any cutting task to immobilize the chain in case of kickback or loss of control. The on/off switch is typically a master control that should be positioned to the run setting during normal operation and to the stop setting when performing maintenance or transporting the tool. The throttle lock and trigger mechanism allow for precise, gradual acceleration, which is essential for maintaining control when starting a cut or responding to changes in wood density. Regular checks of all control linkages for wear, and ensuring the start/stop switch, choke, and throttle return are functioning correctly, will help avoid unexpected engine behavior during demanding forestry or yard tasks.

In practical use, it is critical to maintain a clean, well-lubricated chain and bar while operating the MS 250. The starting and control procedures are interdependent with mechanical condition, so neglecting routine inspection—especially of the ignition system, fuel lines, and carburetor linkages—can lead to hard starting or erratic throttle response. While warming up, perform a brief light-cut to verify that the chain rotates smoothly and that the chain brake releases promptly when the throttle is advanced. Always execute a final check of safety features after maintenance, including the chain catcher, bar nuts, and anti-vibration mounts, to ensure consistent performance across a full range of cutting tasks.

Maintenance and service procedures

Daily maintenance tasks and intervals: Establish a routine that begins with a visual inspection every time you prepare the saw for operation. Check for loose fasteners, damaged guards, and any signs of oil or fuel leaks. Ensure the chain brake functions correctly and that the bar and chain are properly tensioned according to the manufacturer’s specifications. Wipe down the exterior to remove sawdust and debris, and verify that the air intake is clear. For routine operation, lubricate the bar and chain as recommended and replace any worn components before they fail, typically at the end of a standard cutting day or after a defined number of hours of use. Maintaining a clean, dry, and organized work area helps prevent accidental damage and extends the life of critical components. Document all inspections and actions taken to support traceability and future maintenance planning.

Bar and chain inspection and replacement: Begin with a careful visual inspection of the bar rail, groove wear, and chain alignment. Look for burrs, kinks, or missing drive links that can affect cutting efficiency and safety. Measure bar groove wear and assess whether the bar is bent or cracked; replace if any structural damage is evident. Check the chain for stretched rivets, chipped teeth, or signs of excessive wear at the drive sprocket end. Maintain proper chain tension to avoid derailment and uneven cutting. When replacing the bar or chain, ensure the new components match the saw’s specific model and chain pitch, gauge, and drive link count. After installation, perform a test cut in a controlled environment to confirm smooth operation and safe engagement with the clutch system.

Fuel system maintenance and troubleshooting: Use fresh, properly mixed fuel according to the saw’s fuel requirements and avoid prolonged storage of gasoline with ethanol blends that can degrade performance. Inspect the fuel lines for cracks or swelling and confirm that the filter is clean and not obstructed. If starting requires multiple pulls or the engine runs roughly, inspect the carburetor and fuel filter for contamination and consider cleaning or rebuilding as per the service procedures. Check for air leaks around the carburetor boot and ensure that the primer bulb (if equipped) functions correctly. For troubleshooting, verify that the ignition system and spark timing are correct, and replace fuel-related components showing signs of wear. Maintain an orderly fuel storage practice, rotating stock to ensure fuel remains within its recommended shelf life.

Air filter inspection and replacement: Regular inspection of the air intake system is essential to prevent engine damage from dust and debris. Remove the air filter and inspect for visible clogging, tears, or degraded foam; replace if compromised. Clean reusable filters with the recommended solvent and allow full drying before reinstalling, or substitute a new filter if cleaning does not restore airflow. Ensure the carburetor throat is free of obstructions that could restrict air delivery. When reassembling, confirm that the air filter cover seals properly to prevent unfiltered air from entering the combustion chamber. Document the service interval and the condition of the filter to determine replacement frequency based on usage and operating environments.

Spark plug inspection and replacement: Remove and inspect the spark plug for electrode wear, carbon buildup, or grounding issues. Check the gap with the manufacturer’s specified range and adjust only if the plug design allows it; otherwise replace with the correct plug type. Remove any fouling and clean the electrode area carefully, avoiding damage to the ceramic insulator. If the plug shows signs of overheating, oil fouling, or persistent misfiring, replace it to restore reliable starting and smooth operation. Always torque the spark plug to the recommended value and ensure the boot or connector seats firmly to prevent arcing. Maintain a record of spark plug replacements aligned with service intervals and operating conditions to optimize ignition performance.

Lubrication system service and bar oil considerations: Confirm that the bar oil reservoir contains an adequate lubricant level and that the bar oil pump delivers consistent flow during operation. Use the recommended grade of bar oil suitable for the operating temperature range and environmental conditions to prevent bar and chain wear. Inspect oil passages for blockages or leaks and replace seals or gaskets as needed to maintain proper pressure. When conducting lubrication system service, test-run the saw to verify that oil is being distributed along the bar rail evenly, especially in longer cuts. Consider environmental factors such as temperature and humidity, which can affect oil viscosity and pump performance; adjust maintenance schedules accordingly. Always use clean, uncontaminated oil and store oil in approved containers to avoid spoilage or contamination of the system.

The STIHL MS 250 chainsaw requires a systematic approach to diagnosing no-start or hard-start conditions. Begin with a thorough inspection of the fuel system, verifying that the correct fuel mix and oil ratio are used, and that the fuel is fresh and properly stored. Check the spark plug for wear, fouling, or improper gap, and ensure the ignition system delivers a strong, consistent spark. Inspect the air filter for obstructions and clean or replace it as needed. Examine the carburetor for varnish buildup, and consider a clean or rebuild if fuel delivery is suspect. Finally, verify that the recoil start mechanism engages properly and that no components are binding during cranking. A methodical evaluation of these areas will help identify most no-start or hard-start scenarios, and guide corrective actions before more invasive repairs are considered.

Reduced power and performance can stem from several concrete causes, including restricted air intake, degraded spark quality, or improper fuel delivery. Start by confirming the air filter is clean and that the intake path is unobstructed. Inspect the fuel filter and line for cracks, leaks, or collapse, replacing any compromised components. Evaluate the chain brake and throttle lockout to ensure they are not binding and that the engine can reach full RPM. Check the muffler for carbon buildup or obstruction, and remove any obstructions if safe to do so. Finally, verify proper carburetor adjustment within the manufacturer’s specifications and ensure the choke is functioning correctly for the operating temperature. Addressing these factors typically restores expected performance and power output.

Unusual noises and vibration can indicate misalignment, loose fittings, or worn components. Begin with a careful inspection of the chain and bar to confirm proper mounting, lubrication, and tension, and listen for abnormal sounds at idle and under load. Inspect the drive sprocket, clutch assembly, and centrifugal mechanism for wear, scoring, or improper engagement. Check spark plug boot and ignition wiring for moisture or damage that might cause misfiring, which can accompany odd noises. Assess the muffler and exhaust path for restrictions or loose mounting that could create rattling sounds. If vibration persists, also evaluate engine mounts and handle assembly for looseness or cracks. A structured check of these elements will help isolate noise sources and ensure safe, smooth operation.

Chain selection and tensioning are critical for safe and efficient operation of the MS 250. Confirm that the chain pitch matches the bar and that the correct gauge and drive links are installed. Check the chain tension with the chain in a cool, stationary state, and adjust so that the chain sits snugly against the underside of the bar but can still be moved freely by a light touch. Regularly inspect the chain for dull or damaged teeth, missing drive links, or any stiff links that could affect tensioning. Ensure the bar groove is clean and that the bar’s oiling system is delivering lubricant evenly to the chain. After tensioning, perform a quick test by revving the engine and running the chain at low speed to confirm smooth operation without excessive slack or binding. Following these steps will promote safe cutting performance and extend the life of the chain and bar assembly.

Safety first disassembly procedures Disassembly of outdoor power equipment such as the STIHL MS 250 requires strict adherence to safety protocols to prevent injury and damage. Begin by ensuring the engine is completely cooled and the unit is on a stable, clean work surface. Disconnect the spark plug boot to prevent accidental ignition and drain fuel if the model has a fuel‑accessible carburetor system. Gather the appropriate hand tools and organize fasteners by size to avoid misplacement during reassembly. Document each step with clear notes or photos to maintain accurate reference for later inspection. When removing covers and components, apply steady, even pressure and avoid prying hard on fragile tubes or gaskets which could lead to cracks or leaks. Keep the work area well ventilated and free of ignition sources, and dispose of or store fuel in approved containers away from heat sources. Guide bar and chain removal steps Removing the guide bar and chain requires careful attention to tension and sharpness to prevent injury. Begin by relieving chain tension completely and wearing cut-resistant gloves for protection. Remove the chain brake handle or locking mechanism as specified by the service manual, then slide the bar sideward to free the guide bar from the sprocket and studs. Inspect the drive sprocket for wear and rounded teeth, and replace if there is noticeable damage or excessive play. When detaching the chain, note the orientation and ensure the drive link and tie straps are kept aligned to prevent kinking. Clean the bar groove and oiling holes with a small brush, removing any embedded wood fibers or metal shavings. Reinstall the bar and chain with the chain tensions set to a light tightness, verifying that the chain engages the sprocket smoothly and rotates freely by hand. Finally, recheck chain tension after starting the unit and running it briefly, adjusting as needed to maintain safe, proper operation. Carburetor and fuel system inspection The carburetor and fuel system are critical for reliable starting and stable engine performance. Inspect the carburetor body for cracks, gasket integrity, and any signs of fuel leakage around the base or idle mixture screws. Check the fuel lines for hardness, cracks, or deformation, replacing any damaged hoses with manufacturer-approved replacements. Examine the fuel filter for clogging and replace it if it shows signs of restriction or contamination. If the unit exhibits hard starting, high idle, or rich/lean running conditions, consider cleaning the carburetor passages with authorized cleaners and compressed air, taking care not to damage metering diaphragms or jets. After cleaning or replacement, adjust the idle speed and mixture screws according to the service specifications, ensuring stable idle without smokiness or hesitation. Always use fresh, clean, and compatible fuel with the correct oil mix ratio for the model, and store fuel in approved containers away from heat sources. Ignition system inspection and testing A reliable ignition system is essential for safe starts and consistent performance. Begin by disconnecting any electrical connectors and inspecting for corrosion, broken insulation, or loose connections. Remove the flywheel side cover to access the ignition coil and flywheel; check the air gap between the flywheel magnet and the ignition module, ensuring it matches the manufacturer’s specification. Inspect the spark plug for proper electrode gap, fouling, or wear, and replace the plug if it shows signs of wear or contamination. Use a spark plug tester or an inline diagnostic tool to confirm spark strength across a range of compression, noting any weak or inconsistent ignition that could indicate coil or stator problems. If ignition timing is adjustable, set it to the recommended specification and recheck after reinstalling components. After completing inspections, perform a cautious engine test to confirm that the ignition system delivers consistent, reliable starts and smooth operation without misfiring, followed by secure reassembly of all covers and safety shields.

The STIHL MS 250 is a capable chainsaw that relies on a reliable spark plug and ignition system to deliver consistent starts and smooth operation. When servicing the ignition components, begin by disconnecting the spark plug boot to prevent any accidental starts. Inspect the spark plug for electrode wear, fouling, or glazing, and replace it if the electrode gap is out of spec or the insulator is cracked. Use the correct NGK or STIHl-recommended spark plug and verify the correct gap specification before reinstallation. After replacement, thread the plug by hand to avoid cross-threading, then torque to the manufacturer’s specification with a spark plug wrench. Ensure the ignition lead is secure and free from cracks or heat damage, and replace any damaged wires or seals as part of comprehensive ignition maintenance.

Carburetor adjustment on the MS 250 requires careful attention to ensure optimal fuel mixture and engine performance. Begin with a cold engine and use the low, high, and idle needles as defined by the service data for your model year. If the engine runs rich or lean, adjust in small increments, allowing the engine to stabilize after each adjustment. Pay close attention to idle speed, smoke emission, and throttle response during adjustment to avoid stalling or hesitation. When performing a rebuild, inspect the carburetor body for gasket integrity, proper jet sizes, and the condition of the diaphragm and metering needle. Replace worn diaphragms, gaskets, and seals, and ensure the fuel passages are free of debris. Always use fresh, clean fuel and the correct oil mixture to prevent varnish buildup that can affect carburetor function. After adjustments, recheck idle speed and the transition from idle to full throttle to confirm smooth operation across the entire RPM range.

Reassembling after maintenance and safety checks requires a structured approach to ensure engine reliability and operator safety. Begin by reinstalling any removed covers, gaskets, and seals, ensuring all fasteners are torqued to the specified values in a crisscross pattern where applicable. Reconnect the recoil assembly or start mechanism, making sure the rope pull is smooth and returns without binding. Install the spark plug cap firmly, verify the correct ignition timing with model-specific service data, and confirm there are no air leaks around the carburetor or intake manifold. Conduct a thorough safety check, including chain brake function, hand guard integrity, bar and chain lubrication system, and chain tensioning while the bar is stationary. Finally, perform a test run on a stable surface to verify crankcase seals, muffler connection, and overall engine response, watching for abnormal noises, smoke, or overheating. Replace any worn components identified during the test run before returning the saw to service.

The STIHL MS 250 is a compact and reliable chainsaw designed for moderately demanding cutting tasks. Key specifications for reference include a displacement of approximately 45.0 cc, a maximum engine power output around 2.2 horsepower, and a chain speed typical of 14,000 to 15,000 RPM under no-load conditions. The bar length commonly used with this model ranges from 12 to 16 inches, providing a balance between portability and cutting efficiency. Fuel system specifications emphasize a typical two-stroke mixture ratio of 50:1 with high-quality gasoline and oil, along with a calibrated carburetor to sustain stable idle and throttle response. It is important to recognize that ambient conditions, bar and chain lubrication, and chain tension can influence performance, so regular inspection and maintenance are recommended to preserve service life and safety. This section provides tightening torque references and notes essential for correct assembly and reassembly of critical fasteners during servicing or repair.

The torque values for fasteners on the STIHL MS 250 are specified to ensure safe operation and proper component seating. Always consult the manufacturer’s service data for the exact numbers when performing maintenance, as incorrect torque can lead to part failure or unsafe conditions. When tightening cylinder head fasteners, use the recommended sequence and torque progression to evenly load the gasket and avoid warping of the head. For muffler and exhaust-related fasteners, follow the published torque values to maintain exhaust flow and prevent leaks that could affect engine performance. O-rings, gasket seating, and cover screws should be torqued within the specified ranges to ensure proper sealing and to minimize vibration or loosening during operation. Remember to verify torque values after the first startup and during routine maintenance to confirm that vibration has not loosened any fasteners.

Key specifications for reference include rated power output, displacement, and recommended operating conditions that influence torque requirements. The MS 250’s fastener notes emphasize using the correct machine screws, nuts, and washers with appropriate thread lubrication or anti-seize compounds where specified. When replacing or reusing fasteners, inspect for thread damage, corrosion, or elongation, and replace as necessary to maintain integrity. It is essential to clean all fasteners before assembly and apply the correct amount of torque to avoid overstressing components or leaving gaps that could admit dust or moisture. Following these guidelines helps ensure that the saw remains reliable, safe, and capable of delivering consistent performance in the field.

Tightening torque chart and fastener notes provide a concise reference for service technicians. For example, cylinder cover screws may require a modest torque value to prevent leaks while allowing easy removal for maintenance. Bar nut and bar plate fasteners usually call for a higher torque to secure the bar against lateral movement and to maintain proper chain alignment. Chain tensioning screws should be torqued within the specified range to ensure smooth operation without excessive resistance or slack. When working on the air filter cover, maintain a moderate torque to preserve a tight seal without risking deformation of the housing. Always use clean, dry fasteners and avoid cross-threading by aligning fasteners carefully before torquing. Concluding checks should include a re-torque after a few minutes of operation to confirm stability and safety.