Stihl MS390 Chainsaw Manual

The Stihl MS390 is a professional-grade chainsaw featuring a powerful 64.1cc engine, STIHL Quickstop® inertia chain brake, Ematic™ lubrication system, anti-vibration system, side-access chain tensioner, and decompression valve for easier starting. This manual covers essential safety instructions, features, assembly, operation, maintenance, troubleshooting, and specifications to ensure safe and efficient use.

1. Safety Instructions 2. Features at a Glance 3. Assembly & Preparation 4. Specifications 5. Controls & Components 6. Starting & Stopping 7. Operating Instructions 8. Maintenance Schedule 9. Chain & Bar Care 10. Storage Guidelines 11. Troubleshooting

Safety Instructions

Read all instructions before use. Wear appropriate PPE: safety glasses, hearing protection, gloves, chainsaw chaps, and sturdy boots.

Hazard	Precaution
Kickback	Hold saw firmly with both hands; do not cut with tip of bar.
Chain Brake	Engage chain brake when carrying or not in use; test before each use.
Fuel Handling	Use STIHL MotoMix® or mix fuel/oil per manual; no smoking.
Electrical Hazards	Keep away from power lines.
Working Alone	Do not operate alone; inform others of your location.

Features at a Glance

Key components: Engine, Chain Brake lever, Throttle trigger lockout, Master Control lever, Decompression valve, Chain tensioner, Fuel and oil caps.

Feature	Description
Engine	64.1cc, 2-stroke, single cylinder
STIHL Quickstop®	Inertia-activated chain brake for safety
Ematic™ System	Precision chain lubrication for reduced oil consumption
Anti-Vibration	Reduces operator fatigue
Side-Access Tensioner	Easy chain adjustment without tools
Decompression Valve	Reduces pulling resistance for easier starting
Master Control Lever	Single lever for choke, start, and run positions
Fuel Tank Capacity	0.81 US pt (0.38 l)
Oil Tank Capacity	0.51 US pt (0.24 l)

Assembly & Preparation

Unpack and inspect contents. Assemble on a clean, stable surface.

Attach Guide Bar and Chain: Place bar on studs, loop chain over sprocket and bar, adjust tension via side wheel.
Fill Fuel: Use STIHL MotoMix® (50:1 premix) or mix 89 octane gasoline with STIHL HP Ultra oil at 50:1 ratio.
Fill Chain Oil: Use STIHL chain oil or approved substitute; check oiler flow.
Check Controls: Ensure throttle trigger lockout, chain brake, and master control lever function properly.

WARNING! Fuel is highly flammable. Mix and fill in well-ventilated area away from sparks or flames.

Specifications

Displacement: 64.1 cc (3.91 cu. in.)
Power Output: 3.6 kW (4.8 bhp)
Weight (powerhead): 13.2 lbs (6.0 kg)
Fuel/Oil Ratio: 50:1 (STIHL HP Ultra)
Recommended Bar Lengths: 16" to 25"
Chain Pitch/Gauge: 3/8" P, .050" (1.3 mm)
Sound Power Level: 114 dB(A)
Vibration Levels (front/rear): 4.2/2.5 m/s²
Warranty: Limited warranty for personal/commercial use.

Controls and Settings

Master Control Lever: Controls choke (cold start), start, and run positions. Throttle Trigger Lockout: Must be depressed to engage throttle. Chain Brake Lever: Manual engagement; inertia-activated. Decompression Valve: Push to reduce cylinder pressure before starting.

Adjustments: Chain Tension (side wheel), Idle Speed (carburetor screw), Oil Flow (screw near oil cap).

Starting & Stopping

Cold Start:

Engage chain brake. Place on firm ground.
Press decompression valve (if equipped).
Set Master Control to choke position (full up).
Press throttle trigger lockout and squeeze throttle once to set fast idle.
Pull starter handle until engine fires (1-5 pulls).
Move Master Control to half-throttle position.
Pull until engine starts. Blip throttle to return to idle.

Warm Start: Master Control in run position (down). No choke.

Stopping: Release throttle, push Master Control to STOP position.

Operating Instructions

Proper cutting techniques ensure safety and efficiency.

Grip: Hold front handle with left hand, rear handle with right. Thumb under handle.
Stance: Stand with feet shoulder-width apart, left foot slightly forward.
Starting Cut: Apply slight pressure, let chain do the work. Avoid forcing.
Kickback Zone: Do not cut with upper quadrant of bar tip.
Bucking & Limbing: Use appropriate techniques; be aware of pinch points.
Chain Brake Test: Verify operation by engaging manually with saw off.

Tip: Keep chain sharp and properly tensioned. Lubricate continuously during operation.

Maintenance Schedule

Interval	Task
Daily/Before Use	Check chain tension, sharpness, brake function, fuel/oil levels
Every 5 Hours	Clean air filter, check spark plug
Every 20 Hours	Clean spark arrestor screen, check fuel filter
Every 100 Hours	Clean cylinder fins, check clutch and sprocket
Annually	Professional servicing recommended

Chain & Bar Care

Sharpening: Use round file and guide matching chain pitch. Maintain correct filing angle (typically 30°). Depth gauges must be filed periodically.

Bar Maintenance: Clean bar groove regularly. Flip bar weekly for even wear. Lubricate sprocket tip.

CAUTION! Always wear gloves when handling chain. Ensure saw is off and cool.

Storage Guidelines

Long-term storage (over 30 days):

Drain fuel tank and run carburetor dry.
Remove chain, clean, and soak in oil.
Clean entire saw, especially cooling fins and air filter.
Store in dry, cool place, away from ignition sources.
Use fuel stabilizer if fuel cannot be drained.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	No fuel, flooded, spark plug	Check fuel; set Master Control to run; dry plug; check spark.
Engine runs poorly	Dirty air filter, clogged fuel filter	Clean/replace air filter; replace fuel filter.
Chain doesn't turn	Brake engaged, low idle, clutch	Disengage brake; adjust idle speed; check clutch.
Excessive vibration	Loose parts, unbalanced chain	Tighten mounting nuts; balance chain.
Chain throws oil	Over-oiling, wrong oil	Adjust oiler; use correct bar/chain oil.
Chain dulls quickly	Cutting dirt, improper filing	Avoid ground contact; sharpen correctly.

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