Stihl FS40 Trimmer Manual

The Stihl FS40 is a lightweight, professional-grade gasoline-powered trimmer designed for clearing grass, weeds, and light brush. It features a powerful 2-stroke engine with Easy2Start™ technology, a straight shaft with bicycle-style handles for comfort, a PolyCut® head for efficient line cutting, and a range of safety and maintenance features. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: 2-stroke engine, Straight drive shaft, Bicycle-style handlebar, PolyCut® cutting head, Fuel tank, Throttle trigger with lockout, Stop switch.

Feature	Description
Engine	27.2 cc 2-stroke gasoline engine with Easy2Start™ system
Drive Shaft	Straight solid shaft for balanced handling
Handlebar	Bicycle-style with adjustable D-handle for operator comfort
Cutting Head	PolyCut® head for automatic line advance (tap-and-go)
Fuel System	Transparent fuel tank with integrated fuel filter
Throttle	Trigger with lockout to prevent accidental acceleration
Stop Switch	Engine kill switch for immediate shutdown
Spark Arrestor	Muffler with USDA-approved spark arrestor screen
Debris Shield	Protective guard to deflect material from operator
Vibration Dampening	Anti-vibration system in handles and shaft

Assembly & Preparation

Unpack and inspect all parts. Assemble on a clean, flat surface.

1. Attach the handlebar: Slide onto shaft, align, and tighten clamping screws securely.
2. Install the debris shield: Align with mounting points on gearhead and secure.
3. Install the cutting head: Thread the PolyCut head onto the drive shaft (clockwise).
4. Fill with fuel: Use STIHL MotoMix® or mix 50:1 with 89+ octane gasoline and STIHL HP Ultra oil.

WARNING! Fuel is highly flammable. Mix and fill outdoors, away from sparks or flames. Avoid skin contact.

First-Time Operation

Before starting, ensure unit is on a clear, stable surface away from people and obstacles.

1. Prime the engine: Press the fuel pump bulb 5-7 times until fuel is visible.
2. Set the choke: Move lever to cold start (full choke) position.
3. Engage the Easy2Start: Pull the starter rope slowly until resistance is felt, then pull briskly.
4. Warm up: After engine starts, move choke to run position and allow 30 seconds of idle.

CAUTION! Always wear eye protection, hearing protection, long pants, and sturdy boots during operation.

Specifications

• Engine Displacement: 27.2 cc
• Power Output: 0.9 kW (1.2 bhp)
• Fuel Capacity: 0.53 liters (18 fl. oz.)
• Weight (dry): 5.2 kg (11.5 lbs)
• Shaft Type: Straight solid shaft
• Cutting Swath: Up to 43 cm (17 inches) with standard line
• Sound Power Level: 106 dB(A)
• Vibration Levels: Left handle: 4.2 m/s², Right handle: 5.8 m/s²
• Warranty: Limited warranty for residential use (see manual for details)

Controls and Settings

Main controls located on handlebar and engine housing.

Handlebar: Throttle trigger with lockout, Stop switch (I/O), Handle adjustment knobs.

Engine Housing: Choke lever (Cold Start/Run), Fuel pump primer bulb, Air filter cover, Starter grip.

Adjustments: Handlebar height and angle can be adjusted for operator comfort. Throttle cable may require adjustment if engine does not return to idle (consult authorized dealer).

Attachments & Accessories

Compatible with select STIHL attachments (may require adapter).

1. Blade Options: Circular grass blade, 3-tooth brush knife (for heavy weeds).
2. Alternative Heads: AutoCut C 26-2 head, FixCut head for pre-cut line.
3. Harness: STIHL ErgoStart or standard harness for reduced operator fatigue.

Tip: Only use STIHL-approved attachments. Incorrect attachments can cause damage or injury.

Operating Procedures

For trimming grass and light weeds.

1. Starting: Follow First-Time Operation steps. Always hold unit securely.
2. Cutting Technique: Use a smooth, sweeping motion from side to side, keeping head parallel to ground.
3. Line Advance: Tap head firmly on ground while engine is at high RPM (tap-and-go system).
4. Stopping: Release throttle, allow engine to idle for 10 seconds, then press stop switch.
5. Avoiding Damage: Do not force head into dense material. Do not use for edging against hard surfaces.

WARNING! Never operate without debris shield. Keep bystanders at least 15 feet away. Beware of thrown objects.

Safety Features

Throttle lockout: Prevents accidental throttle engagement. Debris shield: Protects operator from flying debris. Stop switch: Immediate engine shutdown. Spark arrestor: Reduces fire risk. Anti-vibration system: Minimizes operator fatigue.

Maintenance & Storage

Perform maintenance with engine off and cool. Use only STIHL replacement parts.

Daily: Clean air filter, check for loose fasteners, inspect cutting head.

Weekly/Monthly: Clean spark arrestor screen, check fuel filter, inspect spark plug.

Storage: For long-term storage, drain fuel tank and run engine until it stops. Store in a dry, secure place.

CAUTION! Never store unit with fuel in tank indoors. Fuel vapors are explosive.

Regulatory Information

EPA and CARB certified for emissions. Complies with ANSI B175.3 safety standards for handheld power tools. This product contains chemicals known to cause cancer and birth defects (California Prop 65). For genuine parts and service, contact an authorized STIHL dealer. © STIHL Incorporated. STIHL is a registered trademark.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded, spark plug	Check fuel level; move choke to run and pull starter; check/replace spark plug.
Engine runs poorly/dies	Clogged air filter, old fuel	Clean or replace air filter; drain and refill with fresh fuel mix.
Line does not advance	Worn line, head jammed	Tap head more firmly on ground; clean head of debris; replace line spool.
Excessive vibration	Loose parts, bent shaft	Tighten all fasteners; inspect shaft for damage (see dealer).
Loss of power	Clogged spark arrestor, carburetor	Clean spark arrestor screen; have carburetor adjusted by dealer.

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

Support: 1-800-467-8445; www.stihlusa.com