Husqvarna FS4800D Service Manual

The Husqvarna FS4800D is a professional-grade, high-performance string trimmer/brushcutter designed for demanding commercial and landscaping applications. This service manual provides detailed technical information, maintenance procedures, troubleshooting guides, and safety instructions for qualified technicians. It covers the FS4800D's engine, fuel system, cutting equipment, drive shaft, gearbox, and electrical system to ensure proper servicing, repair, and optimal performance.

1. Safety Precautions & Symbols 2. Technical Specifications 3. Component Identification 4. Maintenance Schedule 5. Engine Service 6. Fuel System 7. Cutting Equipment & Gearbox 8. Drive Shaft & Bearings 9. Electrical System 10. Troubleshooting Guide 11. Torque Specifications 12. Exploded Views & Parts List

Safety Precautions & Symbols

Before performing any service, disconnect the spark plug cap. Use proper tools and personal protective equipment (PPE).

Symbol	Meaning	Action Required
⚠️	Warning/Caution	Risk of personal injury or damage. Read instructions carefully.
🔥	Fire Hazard	Fuel is flammable. Work in a well-ventilated area away from ignition sources.
⚡	Electrical Hazard	Disconnect spark plug before service to prevent accidental starting.
🛠️	Special Tool Required	Use specified Husqvarna or equivalent service tools.
📖	Refer to Manual	Consult the relevant section of this manual for detailed procedure.

WARNING! Service should only be performed by trained personnel familiar with Husqvarna equipment and safety standards.

Technical Specifications

Model: Husqvarna FS4800D
Engine Type: 2-stroke, air-cooled
Displacement: 75.6 cm³ (approx.)
Power Output: High-performance commercial grade
Fuel/Oil Mix Ratio: 50:1 (Husqvarna XP+ 2-stroke oil recommended)
Fuel Tank Capacity: 1.0 liter (approx.)
Drive System: Solid drive shaft with anti-vibration features
Gearbox Ratio: Optimized for high torque output
Cutting Equipment: Compatible with trimmer heads, metal blades, and brush knives
Starter System: Smart Start® with combined choke/stop control
Ignition System: Electronic (CDI)
Weight (without cutting attachment): Approximately 10.1 kg

Component Identification

Key serviceable components: Throttle handle, control cables, fuel tank, carburetor, air filter, spark plug, muffler, starter assembly, drive shaft, gear housing, cutting attachment interface.

Upper Shaft: Contains throttle trigger, stop switch, and drive shaft connection.
Engine Unit: Houses cylinder, piston, crankshaft, carburetor, and ignition module.
Drive Shaft Tube: Encloses the solid drive shaft connecting the engine to the gearbox.
Gear Housing: Contains bevel gears to transfer power to the cutting head at a 90-degree angle.
Cutting Attachment Guard & Interface: Secures the trimmer line head, blade, or brushcutter attachment.

Maintenance Schedule

Interval (Operating Hours)	Task	Reference Section
Daily / Before Use	Check for loose parts, leaks, and cutting attachment security. Clean air intake on starter and cooling fins.	Section 2, 7
25 Hours	Clean air filter. Check spark plug condition and gap.	Section 6
50 Hours	Clean fuel filter (in tank). Check fuel lines for cracks. Clean carburetor strainer (if equipped).	Section 7
100 Hours	Replace spark plug. Clean cooling system (fins, cylinder cover). Check gearbox grease.	Section 6, 8
300 Hours or Annually	Replace fuel filter. Inspect and clean carburetor (full service). Check drive shaft bearings. Inspect/replace anti-vibration elements.	Section 7, 8, 9

Note: Intervals may vary based on operating conditions (dusty, heavy brush).

Engine Service

Procedures for top-end service: cylinder, piston, and rings.

Spark Plug: Remove with spark plug wrench. Check electrode gap (0.5 mm / 0.020"). Clean or replace.
Cylinder & Piston Inspection: Remove muffler to inspect piston through exhaust port. Look for scoring or excessive carbon.
Cylinder Head Removal: Remove screws, lift off head. Check combustion chamber for carbon deposits.
Crankcase Seals: Inspect for leaks. Replacement requires splitting the crankcase.
Carburetor Adjustment (HSA, H, L screws): Use tachometer for final idle (~2700 RPM) and max no-load speed (specified in tech data).

CAUTION! Always use a torque wrench when reassembling engine components. Refer to Section 11 for specific values.

Fuel System

Includes fuel tank, lines, filter, and carburetor (Zama or Walbro).

Fuel Tank Removal: Drain fuel. Disconnect fuel line and vent hose. Remove mounting screws.
Fuel Filter Replacement: Extract old filter from tank using a wire hook. Connect new filter to fuel line.
Carburetor Removal/Service: Disconnect throttle linkage and fuel line. Remove mounting nuts. Disassemble diaphragm cover, check diaphragms for stiffness/holes, clean jets with compressed air (never wire).
Fuel Line Replacement: Use ethanol-resistant line. Ensure proper routing to avoid kinks.

WARNING! Use only fresh, properly mixed fuel. Stale fuel is a common cause of starting and performance issues.

Cutting Equipment & Gearbox

Service for gear housing, cutting head, and blade mounting.

Gear Housing Grease: Remove cover screws. Pack with high-quality lithium-based grease. Reinstall cover, ensuring seal is intact.
Cutting Attachment Installation: Use correct blade washer and retaining nut. Tighten nut securely with wrench while holding shaft.
Trimmer Head Replacement: For Speed-Feed® type heads, follow specific loading instructions. Ensure head clicks securely onto drive spline.
Shaft Locking: Use shaft locking tool (Husqvarna 502 50 41-01 or equivalent) to immobilize shaft when removing cutting attachments.

Tip: Always balance metal blades before use to prevent excessive vibration.

Drive Shaft & Bearings

Inspection and replacement of drive shaft and support bearings.

Drive Shaft Removal: Separate shaft tube from engine and gear housing. Slide out drive shaft.
Bearing Inspection: Check support bearings in the shaft tube for smooth rotation. Replace if rough or noisy.
Flexible Coupling: Inspect rubber coupling at engine end for cracks or wear. Replace in pairs if damaged.
Reassembly: Lubricate shaft splines with grease before reassembly. Ensure all bearings are seated properly.

Electrical System

Testing and service of ignition (CDI) module, stop switch, and wiring.

Component	Test Procedure	Specification/Result
Spark Plug Cap & Wire	Resistance check	Approx. 5 kΩ
Ignition (CDI) Module	Output check with spark tester	Strong, consistent spark across 7mm gap
Stop Switch (Wires)	Continuity test	Circuit closed (0 Ω) when switch is pressed; open when released.
Choke/Stop Control Lever	Visual and mechanical inspection	Must move freely and return to OFF/RUN position.

Note: The CDI module is non-adjustable and non-serviceable. Replace if faulty.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
Engine will not start	1. No spark 2. Fuel issue (old fuel, clogged filter) 3. Flooded engine 4. Faulty choke mechanism	1. Check spark plug, wire, CDI. 2. Use fresh fuel mix, replace filter. 3. Remove plug, dry cylinder, pull starter with throttle open. 4. Inspect choke linkage and carburetor choke valve.
Engine starts but dies	1. Clogged fuel tank vent 2. Dirty carburetor 3. Air leak (crank seals, gaskets)	1. Clean or replace tank vent. 2. Service carburetor. 3. Perform pressure/vacuum test on crankcase.
Loss of power	1. Clogged air filter 2. Exhaust port/muffler blocked 3. Worn piston/rings 4. Incorrect carb adjustment	1. Clean/replace filter. 2. Clean carbon from exhaust system. 3. Inspect cylinder & piston. 4. Adjust H and L screws per manual.
Excessive vibration	1. Unbalanced cutting blade 2. Bent drive shaft 3. Worn gearbox bearings 4. Loose engine or handle mounting	1. Balance or replace blade. 2. Inspect and replace shaft. 3. Service gear housing. 4. Tighten all mounting bolts.
Cutting attachment does not spin	1. Broken drive shaft 2. Stripped gear in gearbox 3. Clutch slipping (if equipped)	1. Replace drive shaft. 2. Open gear housing, inspect gears. 3. Check clutch springs and shoes.

Torque Specifications

Critical fasteners must be tightened to specified values.

Cylinder Head Screws: 10 Nm (88 in.lb)
Spark Plug: 25 Nm (18.4 ft.lb)
Muffler Mounting Screws: 8 Nm (71 in.lb)
Gear Housing Cover Screws: 4 Nm (35 in.lb)
Cutting Attachment Retaining Nut: 35-40 Nm (26-30 ft.lb) - Use shaft lock tool.
Engine Mounting Bolts: 20 Nm (14.8 ft.lb)
Handle Mounting Bolts: 15 Nm (11 ft.lb)

IMPORTANT: Use a calibrated torque wrench. Do not over-tighten.

Exploded Views & Parts List

Refer to official Husqvarna spare parts catalog for FS4800D for complete diagrams and part numbers. Key assembly groups:

Engine Assembly (Crankcase, Cylinder, Piston)
Fuel System Assembly (Tank, Carburetor, Lines)
Starter Assembly (Recoil starter, pulley, spring)
Drive Shaft Assembly (Shaft, tube, bearings, couplings)
Gear Housing Assembly (Gears, seals, bearings, cover)
Handle & Control Assembly (Handlebar, throttle cable, switches)

Parts Ordering: Always use genuine Husqvarna replacement parts to ensure compatibility, performance, and safety. Contact an authorized Husqvarna service dealer or use the online parts look-up with your model and serial number.