Stihl Weedeater FS 40 C Manual

The Stihl FS 40 C is a lightweight, professional-grade string trimmer (weedeater) featuring a 27.2cc 2-stroke engine, Easy2Start™ system, ErgoStart™, a solid drive shaft, a loop handle, a PolyCut® head, and a translucent fuel tank. It is designed for trimming grass, weeds, and light brush in residential and commercial applications. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

1. Features at a Glance 2. Safety Information 3. Assembly & Preparation 4. Specifications 5. Controls and Components 6. Starting & Stopping the Engine 7. Operating Instructions 8. Maintenance Schedule 9. Storage 10. Warranty Information 11. Troubleshooting

Features at a Glance

Key components: 2-stroke engine, Easy2Start™ system, ErgoStart™, solid drive shaft, loop handle, PolyCut® head, translucent fuel tank, and throttle trigger lockout.

Feature	Description
Engine	27.2cc 2-stroke, air-cooled
Starting System	Easy2Start™ for reduced pulling effort
ErgoStart™	Reduces starter cord resistance
Drive Shaft	Solid shaft for efficient power transfer
Handle	Loop handle for two-handed control
Cutting Head	PolyCut® head for easy line advance
Fuel Tank	Translucent for easy fuel level check
Throttle Trigger Lockout	Prevents accidental throttle engagement
Spark Arrestor Muffler	Reduces fire risk
Weight	Approx. 10.1 lbs (4.6 kg) without cutting attachment

Safety Information

Read all instructions before use. Wear appropriate PPE.

Personal Protective Equipment: Always wear safety glasses, hearing protection, long pants, sturdy boots, and gloves.
Clear Work Area: Remove stones, sticks, wire, and other debris that could be thrown.
Fuel Safety: Refuel outdoors, with engine off and cool. Use clean, fresh fuel mix (50:1 gasoline to STIHL HP Ultra oil).
Operation: Keep bystanders and pets at least 50 feet away. Do not operate in wet conditions.

WARNING! Risk of serious injury or death from rotating cutting line. Keep hands and feet away from cutting attachment at all times.

Assembly & Preparation

Unpack and inspect contents. Assemble according to instructions.

Attach Shaft: Connect upper and lower shaft sections; tighten clamp securely.
Install Handle: Slide loop handle onto shaft; position for comfortable grip; tighten screws.
Install Cutting Attachment: Attach PolyCut® head or other approved accessory; secure with retaining nut.
Fuel Mix: Prepare 50:1 mix with 89 octane gasoline and STIHL HP Ultra oil. Fill tank.

CAUTION! Ensure all fasteners are tight before operation. Use only STIHL-approved attachments.

Specifications

Engine Displacement: 27.2 cc
Engine Type: 2-stroke, single cylinder
Power Output: 0.9 kW (1.2 bhp)
Fuel/Oil Ratio: 50:1 (STIHL HP Ultra)
Fuel Tank Capacity: 14.9 fl oz (0.44 liters)
Sound Pressure Level: Approx. 94 dB(A)
Vibration Level: Left/Right: 4.5/5.5 m/s²
Cutting Swath: Up to 17 inches (with PolyCut head)
Warranty: Limited warranty for residential use

Controls and Components

Main controls located on handle and engine housing.

Handle Area: Throttle trigger, throttle trigger lockout, stop switch.

Engine Housing: Starter grip, choke lever, fuel tank cap, air filter cover, spark plug.

Operation: Depress throttle trigger lockout to enable throttle. Squeeze throttle trigger to increase engine speed. Release to idle. Press stop switch to stop engine.

Starting & Stopping the Engine

Follow proper procedure to avoid flooding and ensure safe operation.

Cold Start: Set stop switch to "I". Move choke lever to closed position. Press fuel primer bulb 5 times. Pull starter cord slowly until resistance is felt, then pull briskly. After engine fires, move choke lever to open position. Pull starter cord again to start.
Warm Start: Choke lever open. Pull starter cord.
Stopping: Release throttle trigger. Press stop switch to "0".

Tip: Do not pull starter cord more than 10 times with choke closed to avoid flooding.

Operating Instructions

Use a smooth, sweeping motion for best results.

Starting Position: Hold unit firmly with both hands, feet shoulder-width apart.
Cutting Technique: Swing trimmer from side to side in an arc, keeping cutting head parallel to ground. Advance slowly.
Line Advance: Tap PolyCut® head on ground (at operating speed) to advance fresh line.
Edging: Rotate unit 90° so cutting line is vertical for edging along sidewalks.
Avoiding Damage: Do not force trimmer. Do not use for cutting woody plants or dense brush.

WARNING! Never operate with one hand. Always maintain secure footing.

Maintenance Schedule

Regular maintenance ensures performance and longevity.

Interval	Task
Before each use	Check for loose fasteners, damage. Clean air filter if dirty.
Every 25 hours	Clean spark arrestor screen. Check spark plug.
Every 50 hours	Replace spark plug. Clean fuel filter. Check fuel lines.
Annually	Have unit serviced by authorized STIHL dealer.

CAUTION! Disconnect spark plug boot before performing any maintenance.

Storage

Prepare unit for storage to prevent fuel system issues.

Short-term (under 30 days): Run engine until fuel tank is empty.
Long-term: Drain fuel tank and carburetor completely. Run engine until it stops. Remove spark plug, add 1 teaspoon of engine oil into cylinder, pull starter cord slowly 2-3 times, reinstall plug. Store in cool, dry place.

CAUTION! Never store unit with fuel in tank for extended periods. Fuel can degrade and damage carburetor.

Warranty Information

STIHL Limited Warranty: Residential use warranty period as defined by local STIHL dealer. Commercial use may have different terms. Proof of purchase required. Warranty does not cover damage from misuse, neglect, improper fuel, or unauthorized modifications. For warranty service, contact an authorized STIHL servicing dealer.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded, spark plug faulty	Check fuel level. Wait if flooded; start with choke open. Check/clean/replace spark plug.
Engine runs poorly, lacks power	Dirty air filter, clogged fuel filter, old fuel	Clean air filter. Replace fuel filter. Use fresh fuel mix.
Cutting line does not advance	Line too short, head jammed	Tap head firmly on ground at speed. Disassemble head to remove debris if jammed.
Excessive vibration	Loose parts, bent drive shaft, unbalanced cutting attachment	Tighten all fasteners. Inspect shaft and attachment for damage.
Unit stops during operation	Overheating, clogged cooling fins, faulty ignition	Allow to cool. Clean cooling fins. Check for spark.

Service: For repairs not covered here, contact an authorized STIHL dealer.

Support: Visit www.stihlusa.com or call 1-800-467-8445.