Stihl MS250 Chainsaw Service Manual

The Stihl MS250 is a professional-grade, lightweight chainsaw featuring a 45.4 cc engine, Easy2Start™ system, anti-vibration handles, Ematic™ lubrication, Quickstop® inertia chain brake, and STIHL Oilomatic® saw chain. This manual provides essential information for safe operation, routine maintenance, troubleshooting, and repair procedures to ensure optimal performance and longevity of your chainsaw.

Safety Information & Warnings

Operating a chainsaw involves serious risks. Always read and understand the owner's manual before use. Wear proper Personal Protective Equipment (PPE): helmet, eye protection, hearing protection, gloves, chainsaw chaps, and sturdy boots.

Hazard	Precaution
Kickback	Always hold saw firmly with both hands; use reduced-kickback chain; do not saw with tip.
Chain Brake	Ensure Quickstop® inertia brake functions correctly before each use.
Fuel Handling	Use only STIHL MotoMix® or fresh fuel/oil mix (50:1); no refueling near open flames.
Hot Surfaces	Avoid contact with muffler and cylinder during/after operation.
Falling Debris	Be aware of your surroundings, especially when felling trees or cutting overhead.

Specifications & Features

• Engine Displacement: 45.4 cc, 2-stroke, single cylinder.
• Power Output: 2.6 kW (3.5 bhp).
• Fuel/Oil Mix: 50:1 (STIHL HP Ultra or equivalent).
• Guide Bar Lengths: 16" or 18" (standard).
• Chain Pitch/Gauge: 3/8" PMM, .050" gauge (STIHL Oilomatic®).
• Ignition System: Electronic, capacitor discharge.
• Starting System: Easy2Start™ with decompression valve.
• Weight (powerhead): 5.2 kg (11.5 lbs).
• Anti-Vibration: STIHL Advanced Damping System.
• Lubrication: Ematic™ system with adjustable oil pump.

Component Identification

Key components: Front Hand Guard with Chain Brake, Throttle Trigger, Throttle Trigger Lockout, Master Control Lever (Stop/Choke/Run), Decompression Valve, Fuel Tank Cap, Oil Tank Cap, Muffler, Spark Plug, Chain Tensioner, Guide Bar, Saw Chain, Chain Catcher.

WARNING! Familiarize yourself with all controls before operation. Ensure chain brake is disengaged before starting.

Assembly & Initial Setup

Unpack and inspect contents. Assemble guide bar and chain.

1. Attach Guide Bar: Place bar over studs, align chain with sprocket, ensure drive links engage.
2. Install Chain: Fit chain over bar, ensuring cutting teeth face forward on top.
3. Install Clutch Cover: Align cover, tighten nuts finger-tight.
4. Tension Chain: Use side-mounted tensioning screw to achieve proper tension (snug against bar, but pullable by hand).
5. Final Tightening: Hold bar tip up, tighten clutch cover nuts securely.
6. Fill Tanks: Add fuel mix to fuel tank, bar & chain oil to oil tank.

CAUTION! Always wear protective gloves when handling the chain. Chain must be properly tensioned to prevent derailment or excessive wear.

Fuel & Lubrication System

Fuel: Use only high-quality, unleaded gasoline (min. 89 octane) mixed with STIHL HP Ultra oil at 50:1 ratio. Do not use fuel older than 30 days.

Oil Pump Adjustment: The Ematic™ system can be adjusted via the screw on the bottom of the saw. Turn clockwise (+) to increase oil flow for longer bars or hardwoods.

Checking Oil Flow: Run saw at full throttle, pointed at a light surface (cardboard). A fine line of oil should be visible.

Engine Maintenance

Regular maintenance is critical for performance and safety.

1. Air Filter: Clean weekly (more often in dusty conditions). Remove, tap clean, or wash in soapy water. Dry completely before reinstalling.
2. Spark Plug: Check gap (0.020" / 0.5 mm) monthly. Clean electrodes or replace if worn (STIHL part # 0000-400-1300).
3. Fuel Filter: Replace annually or if clogged. Use STIHL replacement filter.
4. Cylinder Fins & Muffler: Keep clean of sawdust and debris to prevent overheating.
5. Anti-Vibration Elements: Inspect for cracks or deterioration annually.

Guide Bar & Chain Maintenance

Chain Sharpening: Use correct round file size (4.0 mm / 5/32") and file guide. Maintain 30° cutting angle and 10° top plate filing angle. File all cutters to equal length.

Bar Maintenance: Clean bar groove weekly. Flip bar weekly to ensure even wear. Dress bar rails with a flat file if burred.

Chain Tension: Check frequently when new; chain stretches. A properly tensioned chain will not sag from the bar but can be pulled around by hand.

WARNING! A dull or damaged chain increases kickback risk and operator fatigue. Always stop engine before performing chain maintenance.

Starting & Operating Procedures

Cold Start:

1. Engage chain brake. Place saw on firm ground.
2. Press decompression valve (if equipped).
3. Set Master Control Lever to Choke (full down).
4. Pull starter rope slowly until felt resistance, then pull briskly 2-3 times.
5. Move lever to Half-Throttle position (mid-click). Pull until engine fires.
6. Immediately move lever to Run position. Squeeze throttle trigger to idle.
7. Disengage chain brake by pulling hand guard towards you.

Warm Start: Set lever to Run position and pull.

CAUTION! Never drop-start or start the saw above waist height. Keep bystanders at least 15 feet away.

Carburetor Adjustment

The MS250 carburetor has three adjustment screws: L (Low Speed), H (High Speed), and LA (Idle Speed).

1. Initial Setting: Turn both L and H screws clockwise until lightly seated, then counterclockwise 1 turn out.
2. Warm Up: Run saw at full throttle for 10 seconds.
3. Idle Adjustment (LA): Adjust so chain just stops moving at idle. If chain moves, turn LA counterclockwise slightly.
4. High Speed (H): At full throttle, adjust for smooth, peak RPM (use tachometer if available - target ~13,500 RPM no-load). Do not over-lean.
5. Low Speed (L): From idle, quickly squeeze throttle. Engine should accelerate smoothly without hesitation. If it bogs, turn L counterclockwise slightly.

WARNING! Improper adjustment can cause engine damage. Final adjustment should be performed by a qualified technician with proper equipment.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine will not start	No spark, flooded, stale fuel	Check spark plug; set control to run/half-throttle; use fresh fuel mix; press decomp valve.
Engine starts then dies	Clogged fuel filter, air filter, carb adjustment	Replace fuel filter; clean air filter; check carburetor settings.
Loss of power	Clogged air filter, spark arrestor, improper carb adjustment	Clean air filter; clean spark arrestor screen in muffler; check H screw.
Chain does not oil	Empty oil tank, clogged oil passages, pump adjustment	Fill tank; clean bar groove and oil port; adjust oil pump screw.
Excessive vibration	Loose components, worn AV mounts, unbalanced chain	Tighten all nuts/bolts; inspect AV buffers; sharpen chain evenly.
Chain throws off bar	Improper tension, worn bar, damaged drive sprocket	Retension chain; inspect bar for wear; replace sprocket if worn.

Parts List & Exploded Views

Refer to official STIHL MS250 Illustrated Parts List (IPL) for complete diagrams and part numbers. Key replacement parts include:

• Air Filter: STIHL Part # 0000-120-1605
• Spark Plug: NGK BPMR7A (STIHL # 0000-400-1300)
• Fuel Filter: STIHL Part # 0000-350-3501
• Complete Saw Chain (16"): STIHL Part # 63PM-68
• Guide Bar (16"): STIHL Part # 3003-000-4808
• Drive Sprocket: STIHL Part # 0000-642-2003

Service: For technical support or to locate an authorized STIHL servicing dealer, visit www.stihlusa.com or call 1-800-467-8445.