Stihl FS 46 Repair Manual

The Stihl FS 46 is a lightweight, professional-grade trimmer/brushcutter designed for demanding vegetation control. This manual provides comprehensive repair, maintenance, and troubleshooting guidance for the FS 46 model, including engine disassembly/assembly, fuel system servicing, ignition system checks, drive shaft and gearhead maintenance, and safety procedures. Below are key sections covering specifications, safety, troubleshooting, step-by-step repairs, and parts identification.

1. Specifications & Identification 2. Safety Precautions 3. Tools & Workshop Requirements 4. Engine Repair 5. Fuel System 6. Ignition System 7. Drive Train & Gearhead 8. Carburetor Adjustment 9. Routine Maintenance 10. Parts Diagrams 11. Troubleshooting Guide

Specifications & Identification

Key identification data: Engine type, serial number location, power output.

Specification	Description
Engine Type	STIHL 2-MIX engine, single-cylinder, air-cooled
Displacement	27.2 cc (1.66 cu. in.)
Power Output	0.9 kW (1.2 bhp) at 9000 rpm
Fuel/Oil Mix	50:1 (STIHL HP Ultra or equivalent)
Idle Speed	2800 rpm
Max. RPM (no load)	11500 rpm
Drive System	Flexible drive shaft, spiral bevel gearhead
Cutting Tools	Trimmer line head, metal blades (optional)
Weight (without tool)	Approx. 5.2 kg (11.5 lbs)
Serial Number Location	On engine housing near muffler

Safety Precautions

Always disconnect spark plug before any repair. Wear protective gloves and eyewear.

Work in a clean, well-ventilated area away from ignition sources.
Use only STIHL-approved replacement parts.
Secure unit in a vise with protective jaws during disassembly.
Label disconnected hoses and wires for correct reassembly.
Replace all gaskets, seals, and lock washers during reassembly.

WARNING! Fuel is highly flammable. Drain fuel tank before servicing fuel system. Allow engine to cool completely.

Tools & Workshop Requirements

Required tools: Torx screwdrivers (T10, T15, T27), socket set (8-13mm), feeler gauges, compression tester, spark tester, carburetor adjustment tool, flywheel puller (STIHL 1122 893 4500).

Clean parts with solvent and dry thoroughly before inspection.
Organize parts in order of removal.
Use torque wrench for critical fasteners (cylinder head, crankcase).
Refer to torque specifications table in section 10.

CAUTION! Do not force components; use proper pullers to avoid damage.

Engine Repair

Cylinder & Piston: Inspect for scoring, carbon buildup. Measure ring end gap (max 0.8mm).
Crankcase: Check for cracks, warping. Replace crank seals if leaking.
Crankshaft: Inspect bearings for smooth rotation; check runout (max 0.05mm).
Muffler: Clean spark arrestor screen; decarbonize exhaust ports.
Decompression Valve: Test for leakage; replace if engine is hard to start.

Fuel System

Components: Fuel tank, filter, lines, carburetor (Zama C1Q-S series).

Fuel Line Replacement: Disconnect lines at tank and carburetor; install new lines with clamps. Fuel Filter: Replace annually or if clogged. Tank Vent: Check valve operation; replace if fuel leaks or tank pressurizes.

Carburetor rebuild kit includes: diaphragms, gaskets, needle valve, filter screen.

Ignition System

Components: Spark plug (Bosch WSR6F or equivalent), ignition module (coil), stop switch, wiring.

Check spark plug: Gap 0.5mm; replace if electrode worn or fouled.
Test ignition module: Use spark tester; replace if no spark.
Air gap: Set between flywheel and ignition module legs (0.3mm).
Stop switch: Test continuity; replace if circuit fails open.

Tip: Always use resistor spark plug to prevent radio interference.

Drive Train & Gearhead

Supports flexible shaft and gearhead maintenance.

Drive shaft: Remove by detaching gearhead and handle; inspect for kinks or wear.
Gearhead disassembly: Remove cutting tool, then housing screws.
Gears: Inspect spiral bevel gears for pitting; replace as set.
Bearings: Check for smooth rotation; replace if rough or noisy.
Grease: Pack with STIHL grease (or high-temperature bearing grease).
Reassembly: Align gears; torque housing screws to 8 Nm.

WARNING! Do not operate with damaged drive shaft; can cause vibration and failure.

Carburetor Adjustment

Adjust with engine at operating temperature. Use STIHL adjustment tool.

Initial settings (screws lightly seated then backed out): L screw - 1 turn out; H screw - 1 turn out. Idle speed screw - set to obtain 2800 rpm idle.

Fine-tune: Adjust L for smooth acceleration; adjust H for max RPM (11500 rpm no load).

Routine Maintenance

Daily: Clean air filter (foam), check for loose fasteners.

Weekly: Inspect spark arrestor, fuel filter, cutting tool wear. Monthly: Grease gearhead, check drive shaft alignment. Annually: Replace fuel lines, decarbonize exhaust, check crank seals.

CAUTION! Use only STIHL-approved lubricants and fuels. Improper mix can cause engine damage.

Parts Diagrams

Exploded views available for: Engine assembly, carburetor, ignition system, gearhead, drive shaft, handle assembly.

Order parts using STIHL part numbers from authorized dealers.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine won't start	No spark, fuel issue, compression	Check spark, fuel flow, compression (should be >100 psi).
Engine runs poorly	Clogged air filter, carb adjustment	Clean/replace filter; adjust carburetor L/H screws.
Loss of power	Exhaust clogged, fuel filter	Clean spark arrestor/muffler; replace fuel filter.
Excessive vibration	Bent drive shaft, unbalanced tool	Inspect drive shaft; replace if bent. Balance cutting tool.
Gearhead overheating	Low grease, damaged gears	Disassemble, inspect gears, repack with grease.

Reset: After repairs, reset carburetor to factory settings and readjust.

Service: For technical support, contact STIHL authorized service center or visit www.stihlusa.com.