STIHL FS 85 Manual

The STIHL FS 85 is a professional-grade gasoline-powered string trimmer/brushcutter designed for demanding clearing and trimming tasks. It features a powerful 2-stroke engine with electronic ignition, a loop handle for two-handed operation, a straight shaft with a gear drive, a tap-action cutting head for easy line advance, and a harness system for operator comfort. Below are key sections for safety, features, assembly, operation, maintenance, and troubleshooting.

Features at a Glance

Key components: 2-stroke engine, Loop handle, Straight drive shaft, Tap-action cutting head (FS 85 C), Gear drive, Carrying harness.

Feature	Description
Engine	STIHL 2-MIX engine for reduced fuel consumption and emissions
Ignition System	Electronic ignition (CDI) for reliable starting
Drive System	Straight shaft with gear drive for power transfer
Cutting Attachment	Tap-action cutting head (FS 85 C) or compatible blades
Handle	Loop handle for two-handed control and operator safety
Carrying System	Harness for comfortable operation and weight distribution
Throttle Trigger	With throttle trigger lockout for safety
Stop Switch	For immediate engine shutdown
Choke/Start Settings	Combined choke/run control lever
Fuel System	Diaphragm carburetor with purge bulb

Assembly & Preparation

Unpack and inspect 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 provided bolts.
2. Install the harness: Connect the harness hooks to the attachment points on the machine.
3. Fit the cutting tool: Attach the tap-action cutting head or approved blade, ensuring it is securely fastened with the appropriate nut and washer.
4. Prepare fuel mix: Use STIHL HP Ultra or equivalent high-quality 2-stroke engine oil. Mix with unleaded gasoline at a 50:1 ratio (2% oil). Shake well.

WARNING! Always wear appropriate Personal Protective Equipment (PPE): safety glasses, hearing protection, gloves, long pants, and sturdy boots. Never operate without proper PPE.

First-Time Operation

Perform pre-operation checks before starting the engine.

1. Check fasteners: Ensure all nuts, bolts, and screws are tight.
2. Inspect cutting tool: Verify the trimmer head or blade is secure and not damaged.
3. Fuel the machine: Fill the fuel tank with the correct 50:1 fuel/oil mixture.
4. Starting procedure: Place the unit on a flat, clear surface. Set the master control lever to cold start (choke) position. Press the fuel pump bulb 5-10 times. Pull the starter rope sharply until the engine fires, then move the lever to the run position and pull again to start.

CAUTION! The cutting tool may spin upon starting. Keep the cutting attachment clear of people, animals, and obstacles during startup.

Specifications

• Engine Type: STIHL single-cylinder 2-stroke with 2-MIX technology.
• Displacement: Approximately 30.1 cm³ (1.84 cu. in.).
• Power Output: Professional-grade power for clearing brush and tough weeds.
• Fuel/Oil Mix: 50:1 (2% oil) with high-quality 2-stroke oil.
• Drive Shaft: Straight, solid shaft.
• Gearbox: Heavy-duty gear drive.
• Standard Cutting Attachment: Tap-action cutting head (FS 85 C).
• Sound Power Level: Complies with applicable directives (wear hearing protection).
• Weight (without cutting tool): Approximately 5.8 kg (12.8 lbs).

Controls and Settings

Master Control Lever: Combines choke, run, and stop functions. Throttle Trigger: Controls engine speed; includes a lockout to prevent accidental operation. Stop Switch: "I" for run, "0" for stop. Throttle Interlock: Must be depressed to allow throttle trigger movement.

Operation: Use the harness to support the machine's weight. Hold the handle firmly with both hands. Swing the cutting tool in a controlled, sweeping arc from right to left (for right-handed operation). Do not use for overhead cutting.

Adjustments: Handle position can be adjusted for operator comfort. Harness straps should be adjusted so the machine hangs comfortably without straining the operator.

Attaching Cutting Tools

Supports tap-action trimmer heads and approved metal blades for clearing brush.

1. Ensure the engine is OFF and cool.
2. Use the appropriate shaft locking tool to immobilize the drive shaft.
3. For the tap-action head: Screw it onto the drive shaft thread by hand, then tighten securely with the spanner.
4. For circular blades: Place the blade on the output flange, install the washer and nut. Tighten firmly with the spanner while holding the shaft locked.

Tip: Always use the STIHL recommended cutting attachments and ensure they are balanced and sharp.

Operating Procedures

Designed for trimming grass and cutting light brush.

1. Starting: Follow the cold/hot start procedure. Never drop-start the machine.
2. Trimming: Use the tip of the trimmer line for cutting. Avoid forcing the head into the ground.
3. Brush Cutting: Use a steady, sweeping motion with a sharp blade. Let the blade do the work.
4. Line Advance: Tap the cutting head on the ground (with engine at idle speed) to advance fresh line.
5. Stopping: Release the throttle trigger and allow the engine to idle. Press the stop switch to "0".

WARNING! Always be aware of your surroundings. Keep bystanders and pets at least 15 meters away. Watch for hidden objects like wires, rocks, or nails. Never operate the machine fatigued or under the influence of medication or alcohol.

Maintenance Schedule

Regular maintenance is essential for safety and performance.

Interval	Task
Before each use	Check fasteners, inspect cutting tool, check for fuel leaks.
Daily	Clean air filter, check spark plug condition, clean exterior.
Every 50 hours	Clean fuel filter, check gearbox grease, inspect drive shaft.
Annually or as needed	Replace spark plug, clean/replace muffler screen, have carburetor adjusted by a STIHL dealer.

CAUTION! Always disconnect the spark plug boot before performing any maintenance.

Care & Storage

Clean the machine after each use. For long-term storage, run the carburetor dry or add fuel stabilizer to a full tank. Store in a dry, secure place, out of reach of children.

CAUTION! Fuel is highly flammable. Store fuel in an approved container away from sparks, flames, or heat sources. Never store the machine with fuel in the tank indoors where fumes can accumulate.

Regulatory Information

This machine complies with relevant safety and emission standards. It is intended for professional/commercial use. The warranty is valid only when routine maintenance is performed by an authorized STIHL servicing dealer. For genuine STIHL parts, service, and support, contact your local STIHL dealer or visit www.stihlusa.com.

Troubleshooting

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded, spark plug faulty	Check fuel level and mix. Set control to run, pull starter repeatedly. Check/clean/replace spark plug.
Engine starts but dies	Clogged air/fuel filter, carburetor issue	Clean or replace air filter. Check fuel filter. May require dealer service.
Loss of power	Dirty air filter, clogged muffler	Clean air filter. Clean spark arrestor screen in muffler (if equipped).
Excessive vibration	Loose parts, damaged cutting tool, bent shaft	Tighten all fasteners. Inspect and replace damaged cutting attachment. Check shaft for damage.
Cutting head does not advance line	Line empty, head mechanism jammed	Reload with correct diameter trimmer line. Clean head of debris. Replace if worn.

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