Stihl FS90R Trimmer Manual

The Stihl FS90R is a professional-grade straight-shaft grass trimmer/brushcutter featuring a powerful 2-stroke engine, anti-vibration system, ErgoStart™ for easy starting, loop handle with throttle trigger lockout, adjustable harness, and a versatile cutting head system for nylon line, metal blades, and brush knives. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

1. Features at a Glance 2. Assembly & Setup 3. First-Time Operation 4. Specifications 5. Controls and Functions 6. Attachments & Accessories 7. Operating Procedures 8. Safety Features 9. Maintenance & Storage 10. Warranty Information 11. Troubleshooting

Features at a Glance

Key components: 2-stroke engine, straight drive shaft, loop handle, adjustable harness, cutting head, throttle trigger with lockout, ErgoStart™ system, anti-vibration mounts.

Feature	Description
Engine	2-stroke, single-cylinder, air-cooled
Starting System	ErgoStart™ for reduced pulling force
Anti-Vibration	Integrated dampeners in handle and shaft
Drive Shaft	Straight solid shaft for durability
Cutting Head	Quick-release for line, blades, or brush knives
Handle	Loop handle with throttle trigger lockout
Harness	Adjustable shoulder harness for comfort
Fuel Tank	Integrated with easy-fill cap
Throttle Lock	Prevents accidental throttle engagement
Spark Arrestor	Muffler with USDA-approved spark screen

Assembly & Setup

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

Attach handle: Slide onto shaft, align, tighten clamp screws.
Install harness: Connect D-rings to harness points on unit.
Attach cutting head: Align and secure with retaining nut (use wrench).
Fuel mix: Prepare 50:1 gasoline to 2-stroke oil mix (use STIHL oil).
Fill fuel tank: Use funnel; avoid spills.

WARNING! Wear gloves during assembly. Ensure all fasteners are tight before operation.

First-Time Operation

Before starting, read safety instructions. Perform pre-operation check.

Check fuel: Ensure proper 50:1 mix in tank.
Inspect cutting head: Verify line or blade is secure.
Put on harness: Adjust for comfortable fit.
Start engine: Set stop switch to "I", press throttle lock, pull starter cord.
Warm up: Allow 30 seconds at idle before use.

CAUTION! Clear work area of people, pets, and debris. Wear eye and ear protection.

Specifications

Engine Displacement: 27.2 cc
Power Output: 0.9 kW (1.2 hp)
Fuel Capacity: 0.53 liters (18 fl oz)
Weight: 5.9 kg (13 lbs) without harness
Shaft Type: Straight solid shaft
Cutting Width: Up to 43 cm (17 in) with blade
Sound Pressure: 96 dB(A) at operator's ear
Vibration Level: 4.2 m/s² (left/right handle)
Warranty: 2-year limited warranty

Controls and Functions

Main controls located on handle and engine housing.

Handle: Throttle trigger, throttle lockout, stop switch (I/O). Engine: Choke lever, fuel primer bulb, starter grip, spark plug cover. Harness: Adjustable straps, quick-release buckle.

Operation: Squeeze throttle lock and trigger to increase speed. Release to idle. Use stop switch to shut off engine. Choke for cold starts.

Attachments & Accessories

Compatible with STIHL PolyCut head (line), circular metal blades, brush knives.

Line head: For grass and weeds. Load with 2.4 mm nylon line.
Metal blade: For thick brush, saplings. Use 3-tooth or 80-tooth blade.
Brush knife: For heavy vegetation. Install with retaining nut.

Tip: Always stop engine and disconnect spark plug before changing attachments.

Operating Procedures

Techniques for efficient and safe trimming/brushcutting.

Starting: Set choke, press primer 5x, pull starter until engine fires.
Trimming: Swing trimmer side-to-side in arc, keeping head level.
Brushcutting: Use blade with sweeping motions from right to left.
Stopping: Release throttle, let idle 10 seconds, move stop switch to "O".
Line advance: Tap head on ground at high RPM (bump feed).

WARNING! Never operate above waist height. Watch for hidden obstacles.

Safety Features

Throttle lockout: Prevents accidental throttle engagement. Anti-vibration: Reduces fatigue. Harness: Distributes weight. Spark arrestor: Reduces fire risk. Deflector: Shields operator from debris.

Maintenance & Storage

Regular maintenance ensures long life and safe operation.

Daily: Clean air filter, check for loose parts. Weekly: Inspect spark plug, clean cooling fins. Monthly: Grease drive shaft, check harness. Storage: Drain fuel, run carburetor dry, store in dry place.

CAUTION! Use only STIHL-approved parts and lubricants. Disconnect spark plug before servicing.

Warranty Information

2-year limited warranty for personal use. Warranty covers defects in materials/workmanship. Not covered: normal wear, misuse, improper fuel, unauthorized repairs. For warranty claims, contact authorized STIHL dealer with proof of purchase. For support, visit www.stihlusa.com or call 1-800-467-8445.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine won't start	No fuel, flooded, spark plug	Check fuel; dry plug; replace spark plug.
Engine runs poorly	Dirty air filter, old fuel	Clean/replace filter; use fresh 50:1 mix.
Excessive vibration	Loose parts, bent shaft	Tighten handle/cutter; inspect shaft.
Line not advancing	Empty, tangled, worn head	Reload line; clean head; replace if worn.
Loss of power	Clogged muffler, carburetor	Clean spark arrestor; service carburetor.

Service: Authorized STIHL dealers only. Use genuine STIHL parts.

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