Stihl FS400 Manual

The Stihl FS400 is a professional-grade straight-shaft brushcutter/trimmer designed for demanding vegetation management. It features a powerful 2-stroke engine, anti-vibration system, ergonomic harness system, quick-stop inertia chain brake, easy-start system, and compatibility with a wide range of cutting attachments. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: High-performance 2-stroke engine, Straight shaft with gearhead, Anti-vibration system, Ergonomic harness, Quick-stop inertia chain brake, Easy-start system, and Compatible cutting attachments.

Feature	Description
Engine Type	2-stroke, single-cylinder, air-cooled
Displacement	40.2 cc
Power Output	Professional-grade power output
Fuel System	Diaphragm carburetor
Shaft Type	Straight solid drive shaft
Anti-Vibration	Advanced damping system in handles and shaft
Stopping Devices	Inertia-activated chain brake, throttle trigger lockout
Starter	Easy-start system for reduced pulling effort
Cutting Attachments	Accepts trimmer heads, brush knives, circular saw blades
Harness	Ergonomic dual-point harness included

Safety Instructions

Read and understand all instructions before use. Always wear appropriate PPE.

1. Personal Protective Equipment (PPE): Always wear safety glasses, hearing protection, heavy-duty gloves, long pants, and sturdy boots.
2. Work Area Safety: Clear area of bystanders, especially children and pets. Be aware of hidden obstacles like wires or rocks.
3. Fuel Safety: Refuel outdoors only, with engine stopped and cool. Use approved fuel container. Wipe up spills immediately.
4. Operation Safety: Keep firm footing. Do not operate above shoulder height. Use the harness. Be alert for kickback.
5. Chain Brake: Test the inertia chain brake before each use.

WARNING! Failure to follow safety instructions can result in serious injury or death. The cutting tool can throw objects at high speed.

Assembly & Preparation

Unpack all parts. Assembly requires basic tools.

1. Attach Shaft to Engine: Align shaft with engine coupler and secure with the provided bolts. Tighten to specified torque.
2. Install Handle: Slide the loop handle onto the shaft at a comfortable position and tighten the clamping screws securely.
3. Install Harness: Connect the harness hooks to the attachment points on the machine. Adjust straps for a snug, balanced fit.
4. Install Cutting Attachment: Fit the chosen trimmer head, blade, or saw attachment to the gearhead. Secure with the appropriate locking nut using the combination wrench.
5. Add Fuel & Oil: Mix high-quality 2-stroke engine oil with unleaded gasoline (50:1 ratio for most Stihl oil). Fill the fuel tank.

CAUTION! Ensure all fasteners are tight before operation. Do not force components during assembly.

Specifications

• Engine: 2-stroke, 40.2 cc displacement.
• Powerhead Weight: Approximately 10.1 lbs (4.6 kg) without cutting attachment.
• Shaft Length: Standard straight shaft.
• Fuel Capacity: Approx. 1.3 pints (0.6 liters).
• Oil: Stihl 2-stroke engine oil or equivalent meeting ISO-L-EGD and JASO FD standards.
• Fuel/Oil Ratio: 50:1 (with Stihl oil).
• Sound Pressure Level: Typically 95-105 dB(A). Hearing protection required.
• Vibration Levels: Front/Rear handle vibration values per ISO 22867.
• Cutting Attachment Options: Trimmer heads (e.g., AutoCut), brush knives, circular saw blades.

Controls and Components

Familiarize yourself with all controls before starting.

Main Components: Throttle trigger, Throttle trigger lockout, Stop switch, Choke lever, Primer bulb, Decompression valve (if equipped), Inertia chain brake handle, Handle clamping screws, Shaft, Gearhead, Fuel tank cap, Oil tank cap (if equipped).

Control Functions: - Throttle Trigger: Controls engine speed. Release to idle. - Throttle Trigger Lockout: Must be depressed before throttle can be engaged. - Stop Switch: Move to STOP/0 position to stop engine. - Choke Lever: Use for cold starts. - Primer Bulb: Press 5-10 times to fill carburetor with fuel for cold starts. - Inertia Chain Brake: Automatically activates upon kickback. Can be engaged manually by pushing handle forward.

Starting & Stopping the Engine

Follow these steps precisely.

Cold Start: 1. Place unit on clear, firm ground. 2. Press the fuel tank cap vent (if present). 3. Engage the chain brake by pushing the handle forward until it clicks. 4. Move the stop switch to the RUN/I position. 5. Set the choke lever to FULL CHOKE (closed position). 6. Press the primer bulb 5-10 times until fuel is visible. 7. Hold the unit securely with one hand on the rear handle and foot in the handle bracket. Pull the starter rope briskly until the engine 'fires' (usually 1-3 pulls). 8. Move the choke lever to HALF CHOKE or OPEN position. 9. Pull the starter rope again. The engine should start. 10. Allow to warm up at idle for 30 seconds. Release the chain brake by pulling the handle back.

Warm Start: Do not use choke. Follow steps 1-4 and 9-10.

Stopping: 1. Release the throttle trigger and allow engine to idle. 2. Move the stop switch to the STOP/0 position.

WARNING! Never start the engine without a properly installed cutting attachment. Keep hands and feet clear of the cutting tool.

Operating Instructions

Proper technique ensures efficiency and safety.

1. Harness Use: Always use the harness. Adjust so the tool hangs comfortably with the cutting attachment parallel to the ground.
2. Basic Cutting: Use a smooth, sweeping motion from right to left (for right-handed users). Let the tool do the work; do not force it.
3. Trimming: Use the tip of the line for grass and light weeds. Avoid hitting hard objects like fences or rocks.
4. Brush Cutting: Use a brush knife or saw blade. Use a slow, deliberate cutting action. Beware of kickback.
5. Kickback Zone: Be extremely cautious of the upper quadrant of the cutting attachment (between 12 and 2 o'clock). Do not let this area contact solid objects.
6. Slope Operation: Always stand across the slope, never up or down. Be extra cautious of footing.

Tip: Take frequent breaks to avoid fatigue. Clear debris from the cutting attachment and engine air intake regularly during use.

Maintenance Schedule

Regular maintenance is crucial for performance and longevity.

Interval	Task
Before each use	Check all fasteners for tightness. Inspect cutting attachment for damage. Test chain brake function. Check fuel level.
Daily	Clean exterior and air intake. Check for loose or damaged parts.
Every 25 hours	Clean or replace air filter. Check spark plug condition and gap.
Every 50 hours	Clean spark arrestor screen (if equipped). Check fuel filter. Grease gearhead.
Every 100 hours	Have carburetor adjustments and internal components checked by an authorized STIHL servicing dealer.
As needed	Replace cutting line, sharpen or replace blades, replace worn drive shaft or clutch.

CAUTION! Always disconnect the spark plug boot before performing any maintenance except carburetor adjustments.

Storage

Prepare the unit for storage to prevent fuel system issues.

1. Allow the engine to cool completely.
2. Fuel System Preparation (Long-term storage): Run the engine until it stops to use up fuel in the carburetor. Alternatively, add fuel stabilizer to a full tank and run the engine for 2 minutes to circulate it.
3. Clean the entire unit thoroughly, removing all grass, dirt, and debris.
4. Check for any damage and repair if necessary.
5. Store in a dry, well-ventilated place, out of reach of children. Cover the unit to keep dust off.
6. Remove the cutting attachment or protect the cutting edges.

CAUTION! Never store the unit with fuel in the tank in an enclosed, poorly ventilated area. Fuel vapors are explosive.

Warranty & Support

STIHL Limited Warranty: Refer to the separate warranty document included with your purchase for specific terms and duration. This warranty is valid only for products purchased from an authorized STIHL dealer. For the location of your nearest dealer, service, or genuine STIHL parts, visit www.stihlusa.com or contact STIHL Incorporated customer service.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded engine, dirty air filter, faulty spark plug, choke position incorrect	Check fuel. For flooded engine, move choke to open, hold throttle wide open, and pull starter 10+ times. Clean/replace air filter. Check/replace spark plug.
Engine starts but dies	Clogged fuel filter, dirty carburetor, faulty fuel line, vent in fuel cap blocked	Replace fuel filter. Clean carburetor (may require dealer). Check fuel lines. Clean fuel tank cap vent.
Loss of power	Dirty air filter, clogged spark arrestor, incorrect fuel mix, carburetor needs adjustment	Clean air filter and spark arrestor. Use fresh, properly mixed fuel. Have carburetor adjusted by dealer.
Excessive vibration	Loose fasteners, bent cutting attachment, unbalanced blade, damaged drive shaft	Tighten all nuts and bolts. Inspect and replace damaged cutting attachment or shaft.
Cutting attachment does not spin	Drive shaft disconnected, clutch worn, gearhead damaged, cutting tool jammed	Check shaft connection. Inspect clutch and gearhead (dealer service). Clear jammed debris.

Note: For repairs beyond basic maintenance, contact an authorized STIHL servicing dealer.

Service & Parts: www.stihlusa.com | Find your local authorized STIHL dealer.