Stihl MS 261 C-M Manual

The Stihl MS 261 C-M is a professional-grade chainsaw featuring the innovative M-Tronic engine management system for automatic carburetor adjustment, reduced emissions, and consistent performance under varying conditions. It includes a decompression valve for easier starting, an anti-vibration system, a side-access chain tensioner, and STIHL Quickstop® inertia chain brake. Below are key sections for safety, features, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: M-Tronic engine control unit, Decompression valve, Quickstop® inertia chain brake, Side-access chain tensioner, Anti-vibration system, Tool-free fuel and oil caps.

Feature	Description
M-Tronic Engine Management	Automatically adjusts carburetor for optimal performance in all conditions
Decompression Valve	Reduces cylinder pressure for easier starting
STIHL Quickstop® Inertia Chain Brake	Stops chain rotation in kickback situations
Side-Access Chain Tensioner	Allows easy chain adjustment from the side of the saw
Anti-Vibration System	Reduces vibration to operator's hands
Ematic™ Lubrication System	Efficient chain oil delivery, reduces consumption
Fuel and Oil Caps	Tool-free opening for easy refueling
Chain Catcher	Helps reduce risk if chain breaks or derails
Throttle Interlock	Prevents accidental throttle activation
Master Control Lever	Combines stop switch, choke, and start functions

Safety Information

Read and understand all instructions before operation. Always wear proper PPE.

1. Personal Protective Equipment: Wear safety glasses, hearing protection, gloves, chainsaw chaps/pants, and sturdy boots.
2. Pre-Operation Check: Inspect saw for damage, ensure chain brake functions, check chain tension and sharpness.
3. Work Area Safety: Clear area of obstacles, ensure secure footing, maintain safe distance from others.
4. Fuel Safety: Refuel in well-ventilated area, away from ignition sources. Use STIHL MotoMix® or 50:1 fuel/oil mix.

WARNING! Risk of serious injury or death from kickback, chain contact, or falling limbs. Never operate saw above shoulder height or with one hand.

Assembly & First Use

Assemble guide bar and chain, fill with fuel and oil.

1. Mount guide bar and chain: Loosen bar nuts, position bar, fit chain with cutters facing forward, tension correctly.
2. Fill fuel tank: Use STIHL MotoMix® (pre-mixed) or 50:1 mixture of unleaded gasoline (min. 89 octane) and STIHL HP Ultra oil.
3. Fill chain oil tank: Use STIHL chain oil or equivalent for temperatures above 14°F (-10°C).
4. Initial start: Place saw on clear ground, engage chain brake, set Master Control to cold start position, pull starter cord.

CAUTION! Ensure chain brake is engaged when starting. Keep hands away from chain at all times.

Specifications

• Engine Displacement: 50.2 cc (3.06 cu. in.)
• Power Output: 3.0 kW (4.0 bhp)
• Weight (powerhead): 5.2 kg (11.5 lbs)
• Fuel Tank Volume: 0.5 L (16.9 fl. oz.)
• Oil Tank Volume: 0.26 L (8.8 fl. oz.)
• Recommended Bar Lengths: 16" (40 cm) to 20" (50 cm)
• Chain Pitch/Gauge: 3/8" PMM / .050" (1.3 mm)
• Sound Pressure Level: 106 dB(A)
• Vibration Levels (front/rear): 4.2/2.4 m/s²
• Emissions Compliance: EPA Phase III, EU Stage V

Controls and Components

Front Handle: Contains throttle trigger with interlock and Master Control Lever. Rear Handle: Contains stop switch. Right Side: Chain brake lever, chain tensioner, oil filler cap. Left Side: Fuel filler cap, decompression valve button.

Master Control Lever Positions: STOP (0), RUN (I), COLD START (II), CHOKE (III).

Chain Brake: Manual activation via front hand guard; inertia-activated during kickback. M-Tronic: No manual adjustment needed; system self-calibrates. Decompression Valve: Press before starting to reduce pulling resistance.

Starting & Stopping the Engine

Cold Start:

1. Engage chain brake.
2. Press decompression valve (if equipped).
3. Set Master Control to CHOKE (III).
4. Press purge bulb 6 times until fuel is visible.
5. Place saw on ground, hold rear handle with right foot.
6. Pull starter handle sharply until engine fires.
7. Move Master Control to COLD START (II).
8. Pull starter handle again to start engine.
9. Briefly blip throttle to disengage fast idle.

Warm Start: Master Control in RUN (I) position. No choke needed.

Stopping: Release throttle, move Master Control to STOP (0).

Operation & Cutting Techniques

Always use proper grip: left hand on front handle, right hand on rear handle. Keep body to left of cut line.

1. Felling: Plan escape path. Make notch cut (1/3 diameter), then felling cut (leave hinge wood).
2. Limbing: Work from trunk outward. Support log properly. Cut from top side when possible.
3. Bucking: Support log at both ends. Cut from top side. For pinched chains, use wedges.
4. Kickback Prevention: Maintain secure grip, do not cut with bar tip, keep chain sharp and tensioned.

WARNING! Never cut above shoulder height. Be aware of reactive forces (kickback, push/pull).

Maintenance Schedule

Daily/Before Use: Check chain tension/sharpness, test chain brake, clean air filter, check fuel/oil levels.

Weekly: Clean cooling fins, check spark plug, clean guide bar groove, inspect anti-vibration elements.

Monthly: Clean fuel filter, replace spark plug (if needed), check all nuts/bolts for tightness.

Annually: Have dealer check carburetor (M-Tronic calibration), check clutch and sprocket, full inspection.

CAUTION! Disconnect spark plug wire before performing maintenance. Use only STIHL approved parts.

Chain & Bar Care

Chain Tension: Correct when chain snaps back after pulling from bar groove (not sagging). Adjust via side tensioner when cool.

Sharpening: Use round file matching chain pitch (typically 5/32" for 3/8" PMM). Maintain 30° filing angle. File all cutters evenly.

Bar Maintenance: Clean bar groove weekly. Flip bar monthly for even wear. Dress bar rails with flat file if burred.

Lubrication: Always use proper chain oil. Check oil flow by running saw at high speed over light surface (should throw line of oil).

Storage

Long-term storage (over 30 days):

1. Drain fuel tank and run engine until it stops.
2. Remove chain, clean and soak in oil.
3. Clean entire saw, especially cooling fins and air filter.
4. Store in dry place, cover to prevent dust.
5. For battery models, store battery at 40-60% charge.

CAUTION! Never store with fuel in tank for extended periods. Fuel deteriorates and can damage carburetor.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	No fuel, flooded, spark plug faulty	Check fuel, set Master Control to RUN, pull 10x with throttle open (clear flood), check/replace spark plug.
Engine runs poorly/dies	Dirty air filter, old fuel, clogged fuel filter	Clean/replace air filter, use fresh fuel, replace fuel filter.
Chain doesn't turn	Chain brake engaged, clutch worn, sprocket damaged	Disengage chain brake, inspect clutch and sprocket, replace if worn.
Chain throws oil excessively	Oil pump setting too high	Adjust oil pump (consult dealer for M-Tronic models).
Excessive vibration	Loose components, unbalanced chain, worn AV mounts	Tighten all nuts/bolts, sharpen chain evenly, replace anti-vibration elements.
M-Tronic flashing warning light	System fault	Contact authorized STIHL dealer for diagnosis.

Reset M-Tronic: Start engine, run at full throttle for 1 minute without cutting to allow recalibration.

Service: For repairs beyond basic maintenance, contact authorized STIHL dealer. Find dealer at www.stihlusa.com or call 1-800-467-8445.