Stihl FS45 Manual Repair

The Stihl FS45 is a lightweight, professional-grade string trimmer/brushcutter designed for demanding clearing and trimming tasks. This manual covers essential safety procedures, technical specifications, routine maintenance, troubleshooting, and step-by-step repair instructions for common issues. Below are key sections for safe operation, features, maintenance schedules, disassembly, and repair procedures.

Features at a Glance

Key components: 2-stroke engine, Easy2Start™ system, Ergonomic harness, PolyCut head, solid drive shaft, and anti-vibration system.

Feature	Description
Engine Type	STIHL 2-MIX engine, 27.2 cc displacement
Power Output	0.9 kW (1.2 bhp) at 9000 rpm
Fuel Tank Capacity	0.53 liters
Cutting Width	Approx. 42 cm with PolyCut head
Starting System	STIHL Easy2Start™ for reduced pulling force
Drive Shaft	Solid, with anti-vibration system
Cutting Attachment	STIHL PolyCut head (standard), compatible with blades
Weight (without cutting attachment)	Approx. 5.2 kg
Emissions Compliance	EPA Phase II, EU Stage II
Warranty	Limited warranty, terms apply

Safety Instructions

Always read and understand the operator's manual before use. Wear appropriate PPE.

1. Personal Protective Equipment (PPE): Always wear safety glasses, hearing protection, gloves, long pants, and sturdy boots.
2. Operation Area: Clear work area of bystanders, especially children and pets. Maintain secure footing.
3. Fuel Safety: Refuel in a well-ventilated area with engine off and cool. Use only STIHL MotoMix or 50:1 2-stroke oil mix.
4. Starting & Stopping: Place unit on clear ground. Follow starting procedure. Use stop switch to shut off.
5. Maintenance Safety: Disconnect spark plug boot before performing any maintenance or repairs.

WARNING! Failure to follow safety instructions can result in serious injury or death. The cutting tool can throw objects at high speed.

Technical Specifications

• Engine: STIHL 2-MIX, single cylinder, 2-stroke, air-cooled.
• Displacement: 27.2 cm³.
• Power Output: 0.9 kW (1.2 bhp) at 9000 rpm.
• Idle Speed: 2800 rpm.
• Max. Engine Speed (WOT): 12500 rpm.
• Fuel/Oil Mix: 50:1 (High-quality 2-stroke oil with minimum JASO FD/ISO-L-EGD rating).
• Ignition System: Electronic, capacitor discharge (CDI).
• Spark Plug: Bosch WSR 6 F or equivalent, gap 0.5 mm.
• Carburetor: Zama C1Q-S series, adjustable H, L, LA screws.
• Vibration Damping: Integral anti-vibration system.

Routine Maintenance

Follow maintenance schedule to ensure optimal performance and longevity.

Daily/Before Use: Check for loose fasteners, damaged parts, and fuel/oil leaks. Clean air intake and exterior.

Every 25 Hours: Clean spark arrestor screen (if equipped). Check spark plug condition and gap.

Every 50 Hours: Clean air filter. Replace if damaged. Check fuel filter in tank.

Every 100 Hours: Clean cooling fins. Check carburetor adjustment. Inspect drive shaft and gearhead grease.

Annually/Off-Season: Drain fuel system or add fuel stabilizer for storage. Perform complete inspection.

Troubleshooting Common Issues

Symptom	Possible Cause	Corrective Action
Engine will not start	No fuel, flooded engine, bad spark, clogged air filter	Check fuel level, use correct mix. Pull starter 5-10 times with choke off. Check spark plug and air filter.
Engine starts but dies	Clogged fuel filter, dirty carburetor, improper adjustment	Replace fuel filter. Clean carburetor jets. Adjust L and H screws per manual.
Loss of power	Clogged air filter, fouled spark plug, exhaust port carbon	Clean/replace air filter. Replace spark plug. Decarbonize exhaust port and muffler.
Excessive vibration	Loose fasteners, bent drive shaft, unbalanced cutting head	Tighten all nuts/bolts. Inspect shaft for damage. Replace cutting head or trimmer line.
Line not feeding	Worn or jammed cutting head, incorrect line size	Disassemble head, clean spool. Use only recommended line diameter (2.0 mm).

Carburetor Adjustment & Repair

The Zama C1Q-S carburetor has three adjustment screws: L (low speed), H (high speed), LA (idle).

1. Initial Settings: Gently turn L and H screws clockwise until lightly seated, then back out L 1 turn, H 1 turn.
2. Warm Up: Start engine and allow to run at half throttle for 3-5 minutes.
3. Idle Adjustment: Adjust LA screw for smooth idle (approx. 2800 rpm). Chain must not rotate.
4. Low Speed (L): From idle, quickly open throttle. If engine hesitates, turn L screw counter-clockwise slightly. If engine stumbles, turn clockwise.
5. High Speed (H): At full throttle, adjust H screw for max RPM (not exceeding 12500 rpm). Use tachometer.
6. Final Idle Check: Re-check idle after H adjustment. Engine should return to stable idle.

Carb Cleaning/Repair Kit: Use STIHL kit 0000 350 7001 for diaphragm and gasket replacement.

Fuel System Service

Includes fuel tank, lines, filter, and carburetor.

1. Fuel Filter Replacement: Drain tank. Use hooked wire to remove old filter. Install new filter (STIHL part 0000 350 3501).
2. Fuel Lines: Inspect for cracks. Replace if hardened or leaking. Use STIHL fuel line kit.
3. Tank Vent: Located in fuel cap. Ensure it is not clogged. Clean with compressed air.
4. Carburetor Diaphragm: If engine runs poorly at an angle, replace pump diaphragm in carburetor.

CAUTION! Use only ethanol-free fuel or STIHL MotoMix to prevent carburetor and fuel line damage.

Ignition System Service

Components: Spark plug, ignition module (coil), and stop switch.

1. Spark Plug Test: Remove plug, reconnect boot, ground electrode to cylinder. Pull starter. Look for strong blue spark.
2. Spark Plug Replacement: Gap new plug to 0.5 mm. Install and torque to 25 Nm (18.4 ft-lb).
3. Ignition Module: If no spark, check air gap between module and flywheel (0.3 mm). Replace module if faulty.
4. Stop Switch Wire: Check for continuity. Disconnect wire from module to test if fault is in switch.

Cutting Head & Drive Shaft

Maintenance of the PolyCut head and drive shaft assembly.

1. Line Replacement: Press tabs on head, remove spool. Wind 5-6 meters of 2.0 mm line onto spool. Reassemble.
2. Head Bearing: If head wobbles or is noisy, replace bearing. Remove retaining clip and press out old bearing.
3. Drive Shaft Disconnect: Remove four screws on gear housing. Slide shaft out of engine coupling. Inspect for bends or damage.
4. Gearhead Grease: Remove plug, fill with STIHL gear grease until it emerges from the vent.

WARNING! Always disconnect spark plug before working on cutting attachment.

Parts & Ordering Information

Use genuine STIHL parts for optimal performance and safety.

• Air Filter: Part # 0000 120 1620
• Spark Plug: Bosch WSR 6 F / STIHL # 0000 400 1302
• Fuel Filter: Part # 0000 350 3501
• Carb Repair Kit: Part # 0000 350 7001
• Trimmer Line (2.0 mm): Part # 0000 350 3020
• PolyCut Head Complete: Part # 0000 350 3017

Order from authorized STIHL dealers or online at www.stihlusa.com.

Warranty & Support

STIHL FS45 is backed by a limited warranty. Proof of purchase from an authorized dealer is required.

Warranty Period: Varies by region. Typically 1 year commercial, 2 years residential. See dealer for details.

Warranty Exclusions: Damage from misuse, improper fuel, lack of maintenance, or unauthorized repairs.

Technical Support: Contact your local authorized STIHL servicing dealer.

Customer Service: STIHL Incorporated, 536 Viking Drive, Virginia Beach, VA 23452. Phone: 1-800-467-8445. Website: www.stihlusa.com.