The YJ125S is a 2003 model scooter designed for urban commuting, offering a lightweight and agile platform for riders seeking economical transportation. Known for its reliable air-cooled 125cc engine and automatic Continuously Variable Transmission (CVT), this scooter provides a comfortable riding posture and straightforward operation. The legacy of engineering quality and durability is evident in the YJ125S, making it a practical choice for navigating city environments. Its design prioritizes maneuverability and ease of use, reflecting a commitment to user-friendly vehicles within the commuter scooter segment. This workshop service and repair manual provides comprehensive guidance for the YJ125S. It covers all essential aspects of maintenance, troubleshooting, and repair, including detailed procedures for the engine, fuel system, ignition, transmission, brakes, electrical systems, and chassis. Designed for professional technicians and advanced DIY mechanics, this manual offers in-depth technical specifications, diagnostic charts, and step-by-step instructions for disassembly and reassembly. Its purpose is to assist users in maintaining the optimal performance and longevity of their 2003 YJ125S scooter. 🏷️ Basic Information Identification Make: Yamaha Model: YJ125S Year: 2003 Vehicle Type: Scooter 👋 Introduction Market Position Segment: Lightweight Scooter / Commuter Scooter Target Market: Urban commuters, riders seeking economical and maneuverable transportation. Competitive Analysis Competitors: Honda Dio, Suzuki Address, Kymco Agility, various other 125cc scooters from Japanese and Asian manufacturers. Key Features Features: Reliable air-cooled engine, automatic transmission, comfortable riding posture, lightweight and agile handling for city riding. 📋 Manual Details Coverage Areas Manual Type: Workshop Service Manual / Repair Manual Language: English Format: PDF Download Target Audience: Professional Technicians, Advanced DIY Mechanics 📖 Manual Coverage Systems Covered Engine: Complete disassembly, inspection, assembly, tuning, troubleshooting, and repair of the 125cc engine. Fuel System: Carburetor overhaul, fuel pump, fuel lines, and related components. Ignition System: CDI unit, spark plug, ignition coil testing and replacement. Cooling System: Air cooling system components and maintenance. Transmission: Automatic CVT (Continuously Variable Transmission) system maintenance, belt inspection, roller weights, and clutch assembly. Chassis Frame: Frame inspection, straightening procedures, and component mounting. Suspension: Front fork overhaul, rear shock absorber inspection and replacement. Brakes: Front and rear brake system maintenance, hydraulic lines, caliper overhaul, brake pad replacement, drum brake adjustment. Electrical System: Wiring diagrams, battery, starter motor, lighting system (headlight, taillight, turn signals), horn, instrumentation. Wheels Tires: Wheel bearing replacement, tire inspection, and inflation specifications. Bodywork Trim: Fairing removal and installation, seat, handlebars, and other cosmetic components. Procedures Included Maintenance: Routine service checks, oil changes, filter replacements, spark plug service, chain/belt adjustments, brake bleeding. Troubleshooting: Diagnostic charts for common problems, symptom-based solutions for engine, electrical, and mechanical issues. Repair: Detailed step-by-step instructions for component removal, overhaul, repair, and reinstallation. Disassembly Assembly: Comprehensive guides for full vehicle teardown and reconstruction. Torque Specifications: Critical torque values for all fasteners to ensure proper assembly and prevent damage. Electrical Diagnostics: Testing procedures for electrical components, continuity checks, and fault finding. Technical Depth Depth Level: Comprehensive, covering all aspects from basic maintenance to advanced engine and electrical system repairs. 📊 Manual Specifications File Format File Type: PDF Searchability: Likely text-searchable (dependent on original scan quality) Print Quality: Digital PDF, print quality depends on user's printer. Binding Type: N/A (Digital Download) Paper Type: N/A (Digital Download) Page Count: Estimated 200-300 pages (typical for a 125cc scooter workshop manual) ⚙️ Engine Specifications Primary Engine Engine Type: 4-stroke, OHC, forced air-cooled Displacement: 125cc (approximate, exact may vary slightly) Bore X Stroke: Refer to manual for precise specifications Compression Ratio: Refer to manual for precise specifications Performance Horsepower: Approximately 7-9 HP (typical for this class) Torque: Approximately 7-8 Nm (typical for this class) Fuel System Fuel Delivery: Carburetor (likely Mikuni or Keihin, specific model in manual) Fuel Type: Unleaded Gasoline Ignition Ignition Type: CDI (Capacitor Discharge Ignition) Lubrication Oil Type: Refer to manual for specific API/JASO specification (e.g., SAE 10W-40 API SG or higher, JASO MA) Oil Capacity: Refer to manual for precise capacity (typically around 0.8-1.0 liters) 🔧 Transmission Standard Transmission Type: Automatic, V-belt type Continuously Variable Transmission (CVT) Final Drive: Gear reduction, enclosed Features Clutch Type: Automatic centrifugal clutch 📐 Dimensions Exterior Length: Refer to manual for exact dimensions Width: Refer to manual for exact dimensions Height: Refer to manual for exact dimensions Weights Dry Weight: Approximately 100-110 kg (typical for this class) Wet Weight: Refer to manual for exact specification Payload Capacity: Refer to manual for specification (typically rider + small load) 🛡️ Safety Features Ratings Safety Certifications: Refer to local regulations and certifications for 2003 models. Active Features Brakes: Front disc brake, Rear drum brake (common configuration for this model year). Lighting: Headlight, taillight, brake light, turn signals for visibility. Passive Features Frame Construction: Underbone steel frame for structural integrity. Foot Peg Placement: Designed for rider stability. 💡 Technology Features Infotainment Instrument Cluster: Analog speedometer, fuel gauge, indicator lights (turn signals, high beam, oil pressure). Driver Assistance ABS: Not...