MS390 Stihl Chainsaw Manual

The Stihl MS390 is a professional-grade chainsaw featuring a powerful engine, advanced anti-vibration system, Quickstop chain brake, STIHL Ematic lubrication, and easy-start technology. Designed for demanding cutting tasks, it includes safety features, maintenance guidelines, and operational instructions. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: Engine with electronic ignition, anti-vibration handles, Quickstop inertia-activated chain brake, side-access chain tensioner, STIHL Ematic bar and chain lubrication system, and decompression valve.

Safety Information

Read and understand all safety warnings before operation.

1. Personal Protective Equipment (PPE): Always wear safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots.
2. Clear Work Area: Ensure no bystanders, especially children, are within at least 15 feet (5 m).
3. Inspect Saw: Check for loose parts, damaged chain, proper chain tension, and sufficient fuel/oil before each use.
4. Secure Workpiece: Never cut holding the saw with one hand. Use proper supports.
5. Kickback Awareness: Be aware of the kickback zone (upper quadrant of bar tip). Use reduced-kickback chain and maintain a firm grip.

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

Assembly & Preparation

Unpack and assemble the chainsaw with care.

1. Attach Guide Bar and Chain: Place bar onto studs, loop chain onto sprocket and bar groove with cutters facing forward on top. Tighten bar nuts hand-tight.
2. Adjust Chain Tension: Use side-access wheel to tension chain until it snaps back when pulled from underside of bar. Tighten bar nuts securely.
3. Fill Fuel Tank: Use clean, fresh fuel mix (50:1 gasoline to STIHL HP Ultra or equivalent high-quality 2-cycle oil).
4. Fill Oil Tank: Use STIHL chainsaw bar oil or equivalent.
5. Check Controls: Ensure throttle trigger, throttle trigger lockout, and master control lever function correctly.

CAUTION! Fuel is highly flammable. Refuel in a well-ventilated area with engine off and cool. Wipe up spills immediately.

Specifications

• Model: STIHL MS 390
• Engine Type: Single cylinder, two-stroke, air-cooled
• Displacement: 64.1 cc (3.91 cu. in.)
• Power Output: 4.0 bhp (3.0 kW)
• Idle Speed: 2,800 rpm
• Max. Engine Speed: 13,500 rpm
• Fuel/Oil Ratio: 50:1 (STIHL HP Ultra or equivalent)
• Ignition System: Electronic, capacitor discharge
• Starting System: STIHL Easy2Start™ (if equipped), recoil starter
• Weight (powerhead): Approx. 13.9 lbs (6.3 kg)
• Sound Pressure Level: Approx. 106 dB(A)
• Vibration Levels (front/rear): Approx. 4.5/2.5 m/s²

Controls and Components

Master Control Lever: Combines stop switch, choke, and start positions. Throttle Trigger Lockout: Must be depressed to engage throttle. Chain Brake Lever: Manual activation; inertia-activated. Decompression Valve: Reduces cylinder pressure for easier starting. Side-Access Chain Tensioner: Adjusts chain tension without tools.

Front Handle: Includes throttle trigger and lockout. Rear Handle: Contains master control lever. Muffler: Equipped with spark arrestor screen. Fuel and Oil Caps: Clearly marked. Chain Catcher: Designed to reduce risk if chain breaks.

Starting & Stopping

Cold Start:

1. Engage chain brake by pushing lever forward.
2. Set master control lever to choke position (full down).
3. Press decompression valve (if equipped).
4. Place saw on firm ground, hold rear handle with right foot, grip front handle with left hand.
5. Pull starter rope sharply until engine fires (usually 1-3 pulls).
6. Move master control lever to half-throttle position (mid-position).
7. Pull starter rope again until engine starts. Let run briefly.
8. Blip throttle to disengage fast idle. Chain brake can be disengaged.

Warm Start: Master control lever in run position (horizontal). No choke needed.

Stopping: Release throttle, move master control lever up to STOP position.

Operating Procedures

Proper cutting techniques ensure safety and efficiency.

1. Basic Stance: Stand with feet shoulder-width apart, firm grip with both hands.
2. Starting a Cut: Apply light throttle, let chain touch wood gently, then increase power.
3. Bucking (cutting felled logs): Support log properly. Cut from top down, beware of binding.
4. Felling: Notch cut (1/3 diameter) on fall side, then back cut leaving hinge wood. Use wedges if needed.
5. Kickback Prevention: Do not let the upper quadrant of the bar tip contact wood or other objects. Maintain secure grip.
6. Chain Brake Use: Engage manually before carrying or if kickback occurs. Test function regularly.

Tip: Let the chain do the work; avoid forcing the saw. Keep the chain sharp.

Maintenance Schedule

Regular maintenance ensures longevity and safe operation.

CAUTION! Always disconnect spark plug wire before performing maintenance other than chain tensioning.

Chain & Bar Care

Proper care of cutting equipment is critical.

1. Sharpening: Use correct round file size (typically 5/32" or 4.0mm). Maintain correct filing angle (usually 30°). File all cutters evenly.
2. Depth Gauges: File down depth gauges (rakers) with a flat file and gauge to maintain proper height difference (approx. 0.025").
3. Bar Maintenance: Regularly clean bar groove. Flip bar weekly for even wear. Dress bar rails with a flat file if burred.
4. Lubrication: Ensure oiler is working. Chain should throw a fine line of oil. Adjust oil flow via screw if adjustable.

WARNING! A dull or poorly maintained chain increases kickback risk and operator fatigue.

Storage Guidelines

Prepare saw for storage to prevent fuel system issues.

1. Drain fuel tank and run engine until it stops to clear carburetor. Alternatively, add fuel stabilizer to a full tank and run for 2 minutes.
2. Remove chain and bar, clean thoroughly, and coat with oil.
3. Clean entire saw, especially cooling fins and air intake.
4. Store in a dry, secure place, out of reach of children.
5. For long-term storage, remove spark plug, add a teaspoon of engine oil into cylinder, pull starter slowly to coat, then reinstall plug.

CAUTION! Storing with untreated fuel can cause gumming in the carburetor.

Troubleshooting

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

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