STIHL FS 45 Trimmer Service Manual

The STIHL FS 45 is a lightweight, straight-shaft grass trimmer designed for residential use. This service manual covers essential maintenance, troubleshooting, and repair procedures for the FS 45 model, including the engine, fuel system, cutting head, drive shaft, and safety features. Below are key sections for specifications, maintenance schedules, troubleshooting, disassembly/assembly, and parts identification.

Specifications & Identification

Key components: 2-stroke engine, straight shaft, loop handle, bump-feed cutting head.

Safety Precautions

Always wear appropriate PPE: safety glasses, hearing protection, gloves, long pants, and sturdy boots.

1. Work Area: Clear area of bystanders, especially children and pets.
2. Fuel Safety: Refuel in well-ventilated area, engine off and cool. Use STIHL MotoMix or 50:1 fuel/oil mix.
3. Operation: Keep firm grip, maintain balance, do not overreach.
4. Maintenance: Disconnect spark plug before performing any service.

WARNING! The cutting line and debris can cause serious injury. Always inspect cutting head and shield before use.

Maintenance Schedule

Regular maintenance ensures optimal performance and longevity.

1. Before Each Use: Check for loose fasteners, damaged parts, and fuel/oil leaks.
2. After Each Use: Clean exterior, inspect cutting head and line.
3. Every 25 Hours: Clean air filter, check spark plug, inspect fuel filter.
4. Every 50 Hours: Clean spark arrestor screen (if equipped), check carburetor adjustments.
5. Every 100 Hours: Replace fuel filter, inspect drive shaft and gearhead.

CAUTION! Use only genuine STIHL parts. Incorrect parts can cause damage or unsafe operation.

Fuel System

• Fuel Mix: Use 50:1 mixture of unleaded gasoline (min. 89 octane) and STIHL 2-stroke engine oil.
• Fuel Filter: Located in fuel tank. Replace if clogged or annually.
• Fuel Lines: Inspect for cracks, brittleness, or leaks. Replace as needed.
• Carburetor: Zama C1Q-S series. Adjust idle (LA) and high-speed (H) screws as per manual.
• Primer Bulb: Press several times to fill carburetor with fuel for starting.

Engine (Carburetor & Ignition)

Access engine components by removing the recoil starter and air filter cover.

Spark Plug: NGK BPMR7A (gap 0.5 mm / 0.020 in). Check and clean every 25 hours.

Carburetor Adjustment (at operating temperature):

1. Idle Speed (LA): Adjust so engine idles smoothly and cutting head does not turn.
2. High Speed (H): Factory set. Do not adjust unless necessary for performance.
3. Low Speed (L): Adjust for smooth acceleration from idle.

Ignition System: Electronic ignition module. Check for spark if engine fails to start.

Cutting Head & Drive Shaft

Cutting Head: AutoCut C 5-2. To advance line: Tap head on ground while engine is at high speed.

1. Line Replacement: Remove spool cover, remove old line, wind new line (max 5 m of 2.4 mm line).
2. Drive Shaft: Solid steel shaft. Inspect for bends or damage. Lubricate with STIHL shaft grease annually.
3. Gearhead: Bevel gear design. Check for grease and wear. Replace if gears are damaged.

Tip: Always use genuine STIHL cutting line for proper feed and performance.

Troubleshooting

Common issues and solutions for the FS 45.

1. Engine won't start: Check fuel, spark plug, primer bulb, and choke setting.
2. Engine runs poorly: Clean/replace air filter, check fuel filter, adjust carburetor.
3. Line not advancing: Check for tangled line, worn bump knob, or improper line winding.
4. Excessive vibration: Check for bent shaft, unbalanced cutting head, or loose fasteners.
5. Loss of power: Check muffler spark arrestor screen for clogging.

WARNING! Always disconnect spark plug before troubleshooting mechanical issues.

Disassembly & Assembly

Major component removal procedures.

Torque Specifications

Critical fasteners and their torque values.

• Spark Plug: 20 Nm (15 ft-lb)
• Cylinder Head Nuts: 10 Nm (7.5 ft-lb)
• Muffler Bolts: 10 Nm (7.5 ft-lb)
• Clutch Drum Nut: 40 Nm (30 ft-lb)
• Gearhead Retaining Nut: 35 Nm (26 ft-lb)
• Handle Mounting Bolts: 8 Nm (6 ft-lb)

CAUTION! Overtightening can strip threads; undertightening can cause parts to loosen during operation.

Parts List & Diagrams

Refer to STIHL illustrated parts diagrams for part numbers and assembly views.

Common Replacement Parts:

1. Air Filter: Part # 0000 120 1605
2. Spark Plug: Part # 0000 400 1300
3. Fuel Filter: Part # 0000 350 3501
4. Cutting Line (2.4mm): Part # 0000 350 3005
5. Carburetor Repair Kit: Part # 0000 120 1800

Note: Always provide model and serial number when ordering parts.

Warranty & Support

STIHL Limited Warranty: Covers defects in materials and workmanship for a specified period from date of retail purchase.

Service: Repairs should be performed by an authorized STIHL servicing dealer.