fs90 stihl manual

The STIHL FS 90 is a professional-grade trimmer/brushcutter designed for demanding vegetation control. It features a powerful 2-stroke engine, lightweight construction, a loop handle for operator comfort, a straight shaft with a gearbox, and compatibility with various cutting attachments (trimmer heads, blades). Below are key sections covering safety, features, assembly, operation, maintenance, troubleshooting, and specifications.

Features at a Glance

Key components: 2-stroke engine, Loop Handle, Throttle Trigger with Lockout, Stop Switch, Choke Lever, Fuel Tank, Straight Shaft with Gearbox, and Attachment Interface.

Feature	Description
Engine	STIHL 2-stroke, air-cooled, single-cylinder
Displacement	Approx. 27.2 cm³ (1.66 cu. in.)
Fuel System	Diaphragm carburetor
Ignition System	Electronic, capacitor discharge (CDI)
Handle System	Loop handle with vibration damping
Shaft	Straight, solid drive shaft
Gearbox	Bevel gear for 90° power transmission
Cutting Tools	Accepts trimmer heads, circular blades, brush knives
Weight (without tool)	Approx. 5.4 kg (11.9 lbs)
Sound Power Level	Meets applicable directives (wear hearing protection)

Assembly & Preparation

Unpack all parts. Assemble on a clean, stable surface.

1. Attach the handle: Secure the loop handle to the shaft at the desired position using the supplied bolts.
2. Install the cutting attachment: Ensure the engine is off. Fit the chosen trimmer head or blade onto the gearbox shaft, secure with the appropriate nut using the combination wrench.
3. Fuel mix: Use only STIHL 2-stroke engine oil mixed with unleaded gasoline (50:1 ratio). Shake well in a clean, approved fuel can.
4. Fill fuel tank: Clean area around cap. Add mixed fuel. Do not overfill.
5. Fill chain oil (if using a brushcutter blade): Use STIHL chain oil in the separate oil tank.

WARNING! Fuel is highly flammable. No smoking. Assemble in a well-ventilated area away from sparks or flames.

Starting & Stopping

Wear full PPE: eye protection, hearing protection, gloves, long pants, and sturdy boots.

1. Cold Start: Place unit on firm ground. Press the fuel pump bulb (if equipped) at least 5 times. Move the master control lever to the choke position (full left). Press the throttle trigger lockout and squeeze the throttle trigger once. Pull the starter rope sharply until engine fires. Move master control lever to the half-throttle position. Pull starter rope again to start. Allow to idle briefly.
2. Warm Start: Master control lever in run position (horizontal). Pull starter rope.
3. Stopping: Release throttle trigger. Allow engine to idle. Move the master control lever to the STOP position.

CAUTION! Keep the cutting attachment clear of the ground and obstacles during starting.

Specifications

• Engine Type: STIHL single-cylinder 2-stroke.
• Power Output: Approx. 0.9 kW (1.2 bhp).
• Fuel/Oil Mix: 50:1 (STIHL 2-Stroke Oil).
• Fuel Tank Capacity: Approx. 0.55 liters (18.6 fl. oz).
• Idle Speed: Factory set, approx. 2800 rpm.
• Maximum Powerhead Speed: Approx. 12,500 rpm.
• Drive System: Solid steel shaft, spiral bevel gearbox.
• Sound Pressure Level: Typically 96 dB(A). Wear hearing protection.
• Vibration Level: Front/Rear handle values per ISO 22867.

Controls & Adjustments

Master Control Lever: Choke/Start/Run/Stop. Throttle Trigger: Controls engine speed. Throttle Trigger Lockout: Must be depressed to engage throttle. Stop Switch: Emergency stop. Handle: Adjustable position on shaft.

Adjustments: Carburetor adjustment screws (H, L, LA) are factory set. Only adjust if necessary and if trained. Handle height can be adjusted for operator comfort by loosening mounting bolts.

Cutting Attachments

STIHL PolyCut head: For grass and light weeds. STIHL Metal Blade: For thick weeds, brush, and saplings. Ensure correct guard is installed for each attachment.

1. Always stop engine before changing attachments.
2. Use the combination wrench to secure or remove the attachment nut.
3. Ensure the blade or head is properly seated and tightened to specification.
4. Install the correct cutting attachment guard for the tool being used.

Tip: Use sharp blades and trimmer line for best performance and reduced load on the engine.

Operation & Techniques

Hold unit firmly with both hands. Maintain secure footing and balance.

1. Trimming: Use a smooth, sweeping motion from right to left (for right-handed operators), cutting with the tip of the line. Do not force.
2. Brush Cutting: Use a blade. Employ a scything motion. Cut from the top down on saplings. Beware of kickback.
3. Working Slope: Always stand across the slope, never up or down. Be extra cautious of footing.
4. Clearing: Scan area for rocks, wire, debris that could be thrown or damage the tool.

WARNING! Risk of severe injury from thrown objects and blade contact. Keep bystanders and pets at least 15 meters (50 feet) away. Never operate above shoulder height.

Maintenance Schedule

Daily: Check for loose fasteners, damage. Clean air intake and exterior. Check cutting attachment security and condition.

Weekly/Clean Air Filter: Remove foam air filter, clean in warm soapy water, dry, re-oil with STIHL filter oil. Spark Plug: Clean and check gap (0.5 mm / 0.020 in). Fuel Filter: Replace if clogged. Gearbox Grease: Lubricate gearbox with STIHL special grease after every 25 hours of operation.

Storage

For storage over 30 days: Drain fuel tank and run carburetor dry. Remove spark plug, add a teaspoon of engine oil into cylinder, pull starter slowly 2-3 times, reinstall plug. Clean entire unit. Store in a dry, secure place, out of reach of children.

CAUTION! Fuel left in the carburetor will evaporate and leave varnish deposits, clogging fuel passages.

Safety Symbols & Warnings

Read and understand the manual before use. Wear protective equipment. Beware of thrown objects and blade contact. Keep bystanders away. Do not operate in explosive atmospheres. Beware of carbon monoxide in enclosed spaces. Hot surfaces: Do not touch muffler. Use correct fuel mix. Secure the unit during transport.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded, spark plug	Check fuel, use correct start procedure, check/clean spark plug.
Engine runs poorly, lacks power	Dirty air filter, clogged fuel filter, old fuel	Clean/replace air filter, replace fuel filter, use fresh fuel mix.
Excessive vibration	Damaged cutting attachment, loose parts	Inspect blade/head for damage or imbalance. Tighten all bolts and attachment nut.
Cutting attachment does not spin	Drive shaft, clutch, gearbox	Check for broken drive shaft, worn clutch, or gearbox damage. See authorized dealer.
Engine overheats	Dirty cooling fins, lean fuel mixture	Clean cylinder fins. Check for air leaks. Have carburetor adjusted by dealer.

Service: For major repairs or carburetor adjustment, contact an authorized STIHL servicing dealer.

Support: STIHL Incorporated, Virginia Beach, VA. www.stihlusa.com