MS390 Stihl Chainsaw Manual

The Stihl MS390 is a professional-grade chainsaw featuring a powerful 64.1cc engine, electronic ignition, anti-vibration system, QuickStop® inertia chain brake, STIHL Ematic™ lubrication system, side-access chain tensioner, and a decompression valve for easier starting. This manual covers safety, features, assembly, operation, maintenance, troubleshooting, and specifications. Always read and understand all safety instructions before use.

Features at a Glance

Key components: Engine, guide bar, saw chain, chain brake, throttle trigger, master control lever, fuel and oil tanks.

Safety Information

Personal Protective Equipment (PPE) is mandatory. Unpack and inspect contents.

1. Wear: Safety helmet with face screen/hearing protection, chainsaw protective gloves, cut-resistant leg protection, sturdy boots.
2. Work Area: Clear of obstacles, ensure secure footing, keep bystanders away.
3. Fuel Safety: Mix fuel outdoors, use approved gasoline/oil, store in approved container.
4. Kickback Zone: Avoid contact with upper quadrant of guide bar tip.

WARNING! Failure to follow safety instructions can result in serious injury or death. The chain brake is a safety device; test before each use.

Assembly & Preparation

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

1. Attach Guide Bar & Chain: Place bar on studs, loop chain over sprocket and bar (cutting edges forward on top), adjust tension.
2. Fuel Mix: Use 50:1 mixture of unleaded gasoline (min. 89 octane) and STIHL 2-stroke oil. Shake well.
3. Fill Tanks: Add fuel/oil mix to fuel tank. Fill oil tank with STIHL chain oil.
4. Check Chain Brake: Pull hand guard forward towards bar tip; it should engage with a click. Push back to disengage.

CAUTION! Chain tension correct when snug against bar but can be pulled around by hand. Re-tension after initial use.

Specifications

• Displacement: 64.1 cc (3.91 cu. in.)
• Power Output: 3.6 kW (4.8 bhp)
• Weight (powerhead): 6.6 kg (14.6 lbs) without bar and chain
• Fuel/Oil Ratio: 50:1 (STIHL 2-stroke oil)
• Idle Speed: 2,800 rpm
• Maximum Power Speed: 9,500 rpm
• Sound Pressure Level: 106 dB(A)
• Vibration Level (front/rear handle): 4.5/2.5 m/s²
• Ignition System: STIHL Electronic Ignition (CDI)
• Spark Plug: Bosch WSR 6 F or equivalent, gap 0.020" (0.5 mm)

Controls and Components

Right Side: Throttle trigger, throttle trigger lockout, master control lever (choke/run/stop), rear handle. Left Side: Chain brake hand guard, side-access chain tensioner, decompression valve (press to engage).

Master Control Lever Positions: - STOP (0): Engine off. - RUN (I): Normal operation. - CHOKE (⏚): Cold start position (pull out).

Chain Brake: Engages automatically by inertia or manually by pushing hand guard forward. Disengage by pulling back towards rear handle.

Starting & Stopping

Cold Start:

1. Engage chain brake. Place on firm ground.
2. Press decompression valve (if equipped).
3. Set master control lever to CHOKE (⏚).
4. Press throttle trigger lockout and throttle trigger, set lever to half-throttle position.
5. Pull starter handle until engine fires (usually 2-5 pulls).
6. Move master control lever to RUN (I).
7. Pull starter handle again to start. Let idle briefly.
8. Disengage chain brake by pulling hand guard back.

Warm Start: Master control lever in RUN (I). Follow steps 4, 7, 8.

Stopping: Release throttle, let engine idle. Push master control lever to STOP (0).

Operation & Cutting Techniques

Always use proper grip: right hand on rear handle, left on front. Maintain secure footing.

1. Basic Cut: Apply light pressure, let chain do the work. Avoid forcing.
2. Felling: Plan escape path. Make notch cut (1/3 diameter), then felling cut. Use wedges if needed.
3. Limbing: Work from trunk outward. Support log off ground.
4. Bucking: Cut from top side whenever possible. Beware of tension/compression.
5. Kickback Prevention: Hold saw firmly, do not cut with bar tip, be aware of pinch points.

WARNING! Never operate above shoulder height or with one hand. Be alert for falling branches.

Maintenance Schedule

CAUTION! Perform maintenance only when engine is off and cool. Disconnect spark plug wire for safety.

Chain & Bar Care

Proper lubrication is critical. Sharpen chain regularly.

1. Sharpening: Use correct round file size (typically 5/32" or 4.0mm). Maintain 30° filing angle. File all cutters to equal length.
2. Depth Gauges: File down with flat file to specified height (use gauge).
3. Bar Maintenance: Clean bar groove, flip bar weekly for even wear. Dress rails with flat file if burred.
4. Lubrication: Ensure oiler works, oil port on bar is clear. Use only recommended chain oil.

Tip: A sharp chain reduces effort, improves safety, and extends life of all components.

Storage

For storage over 30 days:

1. Drain fuel tank and run engine until it stops to clear carburetor.
2. Remove chain, clean and soak in oil. Clean bar and sprocket.
3. Clean entire saw, check for damage.
4. Store in dry, cool place, away from ignition sources.

CAUTION! Never store with fuel in tank for long periods. Fuel can degrade and damage engine.

Troubleshooting

Service: For repairs beyond basic maintenance, contact an authorized STIHL servicing dealer. Use only STIHL replacement parts.

Support: STIHL Incorporated, 1-800-467-8445, www.stihlusa.com