Owners Manual Stihl FS90R

The Stihl FS90R is a professional-grade, straight-shaft grass trimmer/brushcutter featuring a powerful 2-stroke engine, Easy2Start™ system, ErgoStart™, anti-vibration system, loop handle, and harness attachment points. It is designed for clearing heavy grass, weeds, and light brush. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: STIHL 2-MIX engine, straight drive shaft, loop handle, ErgoStart™, Easy2Start™, anti-vibration system, quick-stop inertia clutch, and attachment capability for brushcutter blades.

Feature	Description
Engine	STIHL 2-MIX engine for reduced fuel consumption and emissions
Starting System	Easy2Start™ for easier pulling; ErgoStart™ for reduced effort
Drive Shaft	Straight solid shaft for durability and power transmission
Anti-Vibration	Integrated system to reduce operator fatigue
Handle	Loop handle with integrated controls
Clutch	Quick-stop inertia clutch for safety
Fuel System	Transparent fuel tank with integrated filter
Carburetor	Diaphragm carburetor for operation at various angles
Attachments	Compatible with trimmer heads and brushcutter blades
Harness Points	D-rings for attaching a harness

Safety Information

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

1. Personal Protective Equipment (PPE): Always wear safety glasses, hearing protection, sturdy gloves, long pants, and boots.
2. Clear Work Area: Remove stones, sticks, wire, and other debris.
3. Fuel Safety: Refuel outdoors only, with engine off and cool. Use approved fuel container.
4. Operation: Keep bystanders and pets at a safe distance. Always hold unit with both hands.
5. Hot Surfaces: Avoid contact with muffler and cylinder during/after operation.

WARNING! Risk of severe injury or death from blade contact, thrown objects, or fire. Never operate without proper guards and equipment.

Assembly & Preparation

Unpack all parts. Assembly requires attaching the handle, cutting attachment, and harness.

1. Attach Handle: Position loop handle on shaft and secure with provided screws.
2. Install Cutting Attachment: For trimmer line head, follow specific instructions. For blade, ensure correct guard is installed and blade is secured with locking nut.
3. Add Fuel: Use STIHL MotoMix® pre-mixed fuel or mix STIHL 2-stroke oil with unleaded gasoline (50:1 ratio). Fill to marked level.
4. Attach Harness: Connect harness to D-rings on the unit for balanced operation.

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

Specifications

• Engine Type: STIHL single-cylinder 2-stroke with 2-MIX technology.
• Displacement: 27.2 cc.
• Power Output: 0.9 kW (1.2 bhp).
• Fuel/Oil Ratio: 50:1 (using STIHL 2-stroke oil).
• Fuel Tank Capacity: 0.53 liters (18 fl. oz.).
• Sound Pressure Level: Approx. 96 dB(A).
• Vibration Level: Front handle: 4.5 m/s²; Rear handle: 6.5 m/s².
• Drive Shaft: Straight solid shaft.
• Cutting Attachment: Compatible with trimmer heads and brushcutter blades.
• Weight (without cutting attachment): 5.4 kg (11.9 lbs).

Controls and Functions

Main controls located on the handle and engine housing.

Handle Controls: Throttle trigger with lockout, stop switch (I/O).

Engine Housing: Master Control Lever (combines choke, run, and stop positions), fuel primer bulb, Easy2Start™ mechanism, spark plug boot.

Additional Features: Decompression valve (if equipped) to reduce starting effort. Quick-stop inertia clutch disengages cutting tool when throttle is released.

Starting & Stopping the Engine

Place unit on clear, flat ground. Ensure cutting attachment is clear of obstacles.

1. Cold Start: Set Master Control Lever to choke position (✱). Press fuel primer bulb 5-10 times. Pull starter rope smoothly until engine fires. Move lever to run position (兔子 symbol). Pull starter rope again to start.
2. Warm Start: Set Master Control Lever directly to run position. Pull starter rope.
3. Stopping: Release throttle. Move Master Control Lever to stop position (O).

Tip: Do not pull starter rope to its full extent or let handle snap back.

Operating Instructions

Use a balanced, sweeping motion from right to left.

1. Put on all PPE and harness. Start engine as described.
2. Allow engine to warm up at idle for 30 seconds.
3. For trimming: Hold head parallel to ground, slightly above grass. Swing in an arc.
4. For brushcutting: Use a blade suited to material. Use a slicing motion; do not force.
5. Maintain a firm grip with both hands, thumbs wrapped around handle.
6. Take frequent breaks to avoid fatigue.

WARNING! Never operate above waist height. Be aware of kickback zone (tip of blade/line).

Maintenance Schedule

Regular maintenance ensures performance and longevity. Use only STIHL genuine parts.

Interval	Task
Before each use	Check for loose fasteners, damaged parts. Check cutting attachment.
Daily	Clean air filter. Check fuel filter in tank.
Every 50 hours	Replace spark plug. Clean cooling fins. Check clutch.
Every 100 hours	Replace fuel filter. Clean carburetor (by qualified technician).
As needed	Sharpen or replace blade. Replace trimmer line.

CAUTION! Disconnect spark plug boot before performing any maintenance.

Storage

Prepare unit for storage if not used for more than 30 days.

1. Drain fuel tank and run carburetor dry.
2. Remove spark plug, add a teaspoon of engine oil into cylinder, pull starter rope slowly, reinstall plug.
3. Clean entire unit, especially cooling fins and air filter.
4. Store in a dry, secure place, out of reach of children.

CAUTION! Fuel left in carburetor can degrade and cause starting problems.

Warranty Information

STIHL Limited Warranty for residential use: 1 year from date of retail purchase. Commercial/rental use may have different terms. Proof of purchase required. Warranty covers defects in materials and workmanship. Not covered: normal wear, misuse, lack of maintenance, use of non-STIHL parts/fuel. For warranty service, contact an authorized STIHL servicing dealer.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded, bad spark plug, clogged air filter	Check fuel. Set Master Control to run, pull starter 10+ times to clear flood. Check/replace spark plug. Clean air filter.
Engine starts but dies	Clogged fuel filter, dirty carburetor, faulty fuel line	Replace fuel filter. Have carburetor serviced. Check fuel lines.
Loss of power	Clogged air filter, dirty spark arrestor screen, old fuel	Clean air filter. Clean spark arrestor screen. Use fresh fuel.
Excessive vibration	Bent drive shaft, unbalanced blade, loose parts	Inspect shaft and blade. Tighten all fasteners.
Cutting attachment does not spin	Broken clutch springs, worn clutch shoes, drive shaft disconnect	Inspect clutch. Ensure drive shaft is properly engaged.

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

Support: Visit www.stihlusa.com or contact your local STIHL dealer.