MS 261 STIHL Manual

The STIHL MS 261 is a professional-grade chainsaw featuring a powerful engine, advanced anti-vibration system, quickstop chain brake, decompression valve, and STIHL M-Tronic engine management for automatic adjustment to operating conditions. Below are key sections for safety, features, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: Engine with M-Tronic system, anti-vibration handles, quickstop chain brake, side-access chain tensioner, and fuel/oil caps.

Feature	Description
Engine	2-stroke, single-cylinder with M-Tronic engine management
Displacement	50.2 cm³ (3.06 cu. in.)
Power output	3.0 kW (4.0 bhp)
Fuel tank volume	0.50 L (16.9 fl. oz.)
Oil tank volume	0.26 L (8.8 fl. oz.)
Chain pitch	3/8" or .325"
Weight (powerhead)	5.2 kg (11.5 lbs)
Anti-vibration system	Reduces operator fatigue
Quickstop chain brake	Inertia-activated safety feature
Decompression valve	Easier starting

Safety Instructions

Read all instructions before operation. Wear proper PPE.

1. Always wear: Safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots.
2. Clear work area: Remove tripping hazards and ensure secure footing.
3. Inspect saw: Check for damage, loose parts, and proper chain tension before each use.
4. Fuel safely: Refuel outdoors, away from ignition sources, with engine off and cool.

WARNING! Kickback can occur without warning. Keep proper grip and stance. Never operate above shoulder height.

Assembly & Preparation

Assemble guide bar and chain, fill fluids, adjust chain tension.

1. Mount guide bar and chain: Place bar on studs, loop chain over sprocket, align with tensioning pin.
2. Adjust chain tension: Use side-access tensioner; chain should snap back when pulled from bar.
3. Fill fuel: Use STIHL MotoMix or 50:1 gasoline/oil mixture (89 octane minimum).
4. Fill chain oil: Use STIHL chain oil or equivalent; check oiler function.

CAUTION! Use only STIHL-approved fuels and lubricants. Do not over-tighten chain.

Specifications

• Engine Type: 2-stroke single cylinder with M-Tronic.
• Displacement: 50.2 cm³ (3.06 cu. in.).
• Power Output: 3.0 kW (4.0 bhp).
• Fuel/Oil Ratio: 50:1 (STIHL oil) or use MotoMix pre-mix.
• Sound Pressure: 106 dB(A).
• Vibration Levels: Left/Right 3.2 m/s², Front/Rear 2.5 m/s².
• Max. Recommended Bar Length: 20" (50 cm).
• Ignition: Electronic, capacitor discharge.
• Carburetor: Solenoid-controlled diaphragm with M-Tronic.

Controls and Components

Main controls: Throttle trigger, throttle trigger lockout, stop switch, choke knob, decompression valve, chain brake lever, master control lever.

Master Control Lever: Combines choke, start, and run positions. Chain Brake: Manual activation via front hand guard; inertia-activated. Decompression Valve: Reduces cylinder pressure for easier starting. Side-Access Chain Tensioner: Allows adjustment without removing cover.

Starting & Stopping

Cold Start: Engage chain brake, set master control to choke, pull starter until engine fires, move to run position, restart. Warm Start: Master control in run position.

1. Place saw on firm ground, engage chain brake.
2. Press decompression valve (if equipped).
3. Set master control to choke (cold) or run (warm).
4. Hold front handle with left hand, place right foot in rear handle.
5. Pull starter handle briskly until engine fires.
6. Move master control to run position (cold start).
7. Disengage chain brake before cutting.

Stop: Release throttle, press stop switch to "0".

Operating Instructions

Proper cutting techniques to maximize efficiency and safety.

1. Hold saw firmly: Left hand on front handle, right on rear, thumbs wrapped.
2. Stand to left of cut: Keep body out of line with chain.
3. Let saw do the work: Apply light pressure; avoid forcing.
4. Bucking: Support log properly; cut from top unless pinching.
5. Limbing: Stand uphill; cut from opposite side of log.
6. Kickback prevention: Keep nose of bar away from objects; maintain high chain speed.

WARNING! Never cut with upper quadrant of bar tip. Always plan escape path.

Maintenance & Cleaning

Daily and periodic maintenance schedule.

Interval	Task
Before each use	Check chain tension, sharpness, and lubrication
Daily	Clean air filter, check for loose fasteners
Weekly	Clean cooling fins, spark arrestor screen
Monthly	Inspect spark plug, fuel filter, anti-vibration elements
As needed	Replace worn sprocket, bar, chain

CAUTION! Disconnect spark plug before performing maintenance.

Chain & Bar Care

Proper chain maintenance ensures optimal performance and safety.

1. Sharpening: Use round file and guide; maintain correct filing angle (typically 30°).
2. Depth gauges: File to proper height (0.025" / 0.65 mm) using depth gauge tool.
3. Bar maintenance: Clean bar groove, flip bar regularly for even wear.
4. Lubrication: Always use chain oil; adjust oiler as needed for conditions.

Tip: Keep chain sharp; a dull chain increases kickback risk and reduces efficiency.

Storage Guidelines

Proper storage prevents fuel system issues and corrosion.

1. Short-term (under 30 days): Run carburetor dry or add fuel stabilizer.
2. Long-term: Drain fuel tank completely, run engine until it stops. Remove chain, clean entire saw, store in dry place.
3. Chain storage: Soak in oil to prevent rust.

CAUTION! Never store with fuel in tank for extended periods without stabilizer.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	Fuel, spark, compression	Check fuel freshness, spark plug, decompression valve, M-Tronic reset.
Engine runs poorly	Air filter, fuel filter	Clean/replace air filter; replace fuel filter; check fuel lines.
Chain doesn't turn	Brake engaged, clutch, sprocket	Disengage chain brake; inspect clutch drum and sprocket.
Chain lacks oil	Oil tank, oiler, passages	Fill oil tank; check oiler adjustment; clean oil passages.
Excessive vibration	Loose parts, AV mounts	Tighten all fasteners; inspect anti-vibration elements.

M-Tronic Reset: Start engine, run at full throttle for 60 seconds to reset adaptation.

Service: Authorized STIHL dealers only. Visit www.stihlusa.com or contact 1-800-467-8445.