Stihl FS40 Manual

The Stihl FS40 is a lightweight, easy-to-use gasoline-powered string trimmer designed for residential lawn and garden maintenance. It features a curved shaft, a reliable 2-stroke engine with easy-start technology, a Tap Advance™ cutting head for quick line extension, adjustable handle, and a bicycle-style handlebar for comfortable operation. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: 2-stroke engine, curved shaft, Tap Advance™ cutting head, bicycle handlebar, throttle trigger, stop switch, fuel tank, and primer bulb.

Feature	Description
Engine	27.2cc 2-stroke gasoline engine with easy-start system
Shaft	Curved shaft design for balanced trimming
Cutting Head	Tap Advance™ head for bump-feed line extension
Handle	Adjustable bicycle-style handlebar with anti-vibration
Fuel Tank	Transparent tank for easy fuel level check
Throttle Trigger	Lockout for safety; variable speed control
Stop Switch	Quick engine shut-off
Primer Bulb	For easy cold starts
Weight	Approx. 10.1 lbs (4.6 kg) without fuel
Warranty	Limited warranty; see dealer for details

Safety Information

Read all instructions before use. Wear protective gear.

1. Personal Protective Equipment: Always wear safety glasses, hearing protection, long pants, sturdy shoes, and gloves.
2. Clear Work Area: Remove stones, sticks, wire, and other debris before trimming.
3. Fuel Safety: Mix fuel outdoors; store in approved container; no smoking near fuel.
4. Operation: Keep bystanders and pets at least 50 feet away. Do not operate in wet grass.
5. Transport: Carry with cutting head away from body; ensure engine is off and cool.

WARNING! Risk of fire, burn, cut, and projectile injury. Use extreme caution.

Assembly & First Use

Unpack and inspect contents. Assemble handle and cutting head.

1. Attach Handle: Slide handle onto shaft; align and tighten clamp screws.
2. Install Cutting Head: Remove protective cap; thread cutting head onto drive shaft (clockwise). Hand-tighten firmly.
3. Install Guard: Attach debris shield to cutting head housing as directed.
4. Add Fuel: Mix Stihl 2-stroke oil with unleaded gasoline (50:1 ratio). Fill tank.
5. Check Controls: Ensure throttle trigger moves freely; stop switch functions.

CAUTION! Do not force parts. Ensure all fasteners are tight before use.

Specifications

• Engine Type: 2-stroke, single cylinder, air-cooled.
• Displacement: 27.2 cc.
• Power Output: 0.9 kW (1.2 bhp).
• Fuel/Oil Ratio: 50:1 (Stihl 2-stroke oil).
• Fuel Tank Capacity: 14.9 fl oz (0.44 liters).
• Cutting Swath: Approx. 16 inches.
• Line Diameter: 0.095 inch (2.4 mm) recommended.
• Shaft Type: Curved, solid drive shaft.
• Sound Power Level: 106 dB(A).
• Vibration Levels: Left handle: 4.2 m/s²; Right handle: 6.5 m/s².

Controls and Components

Handle Area: Throttle trigger with lockout, stop switch, choke lever, primer bulb.

Engine Area: Spark plug, air filter, muffler, fuel cap, starter grip.

Cutting Head: Tap Advance™ bump knob, cutting line, debris shield.

Operation: Set choke for cold start (lever up), pull starter cord. For warm start, choke off. Use throttle for speed; release to idle. Press stop switch to shut off.

Fuel & Oil Mixture

Use unleaded gasoline (min 89 octane) mixed with Stihl 2-stroke oil at 50:1 ratio.

1. Mix in approved fuel can: Add oil first, then gasoline. Shake well.
2. Fill tank: Use funnel; avoid spills. Wipe any fuel from unit.
3. Storage: Use fuel within 30 days; do not mix more than needed.

Tip: Never use straight gasoline or automotive oil. This will damage engine.

Starting & Operating

Starting procedure (cold engine):

1. Place unit on clear, flat ground.
2. Press primer bulb 5-10 times until fuel is visible.
3. Set choke lever to full choke position (up).
4. Press throttle trigger lockout and throttle; pull starter cord briskly until engine fires.
5. Move choke lever to half-choke; pull cord again until engine starts.
6. Allow engine to warm up at idle for 30 seconds.
7. To stop: Release throttle; press stop switch.

WARNING! Keep hands and feet away from cutting head at all times.

Cutting Head & Line

Tap Advance™ head: Bump knob on ground while engine running to advance line.

1. Line Replacement: Turn knob counterclockwise to open head. Remove spool.
2. Wind New Line: Use 25 feet of 0.095" line. Wind evenly in direction of arrow.
3. Reassemble: Thread ends through eyelets; snap spool back into head.
4. Adjust Line Length: Bump knob to release desired length (max 1/2 inch beyond guard).

CAUTION! Always stop engine and disconnect spark plug before servicing head.

Maintenance

Regular maintenance ensures long life and safe operation.

Item	Frequency	Action
Air Filter	Every 10 hours	Clean with soap/water; replace if damaged.
Spark Plug	Every 50 hours	Check gap (0.020"); clean or replace.
Fuel Filter	Annually	Replace if clogged.
Cutting Head	As needed	Inspect for wear; replace spool if cracked.
Exterior	After each use	Wipe clean; check for loose fasteners.

Storage

For storage longer than 30 days:

1. Drain fuel tank and run engine until it stops.
2. Remove spark plug; add 1 teaspoon of oil through spark plug hole. Pull starter cord slowly to distribute oil.
3. Clean entire unit; store in dry, covered area.
4. Protect from dust and moisture.

CAUTION! Never store unit with fuel in tank indoors or in enclosed space.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	No fuel, old fuel, clogged filter, spark plug	Check fuel; use fresh mix; clean/replace filter; check spark plug.
Engine runs poorly	Dirty air filter, wrong fuel mix, carb adjustment	Clean air filter; ensure 50:1 mix; see dealer for carb service.
Line won't advance	Empty spool, tangled line, worn head	Reload line; untangle; replace spool if damaged.
Excessive vibration	Loose parts, bent shaft, unbalanced head	Tighten all fasteners; inspect shaft; replace head if needed.
Overheating	Dirty cooling fins, low oil mix, clogged muffler	Clean fins; use correct mix; clean muffler screen.

Service: For repairs, contact authorized Stihl dealer. Use only genuine Stihl parts.

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