Positioning:
The Yamaha YJ125S 'Majesty S' (or similar in some markets) was positioned as an accessible, practical, and stylish scooter for urban commuting and short-distance travel, balancing performance and economy.
Competitors:
Competed with other 125cc scooters from Honda (e.g., PCX125, SH125), Suzuki (e.g., Address), Kymco, and SYM in its respective markets.
Features:
Compact and maneuverable design, efficient fuel consumption, comfortable riding position, ample under-seat storage, reliable Yamaha engine technology.
Value:
This workshop manual provides DIY mechanics and technicians with the necessary information to maintain, diagnose, and repair the Yamaha YJ125S 2003, offering significant cost savings over dealership service.
Engine Overhaul:
Complete disassembly, inspection, reassembly, and tuning of the 125cc engine.
Fuel System:
Carburetor adjustment, cleaning, and overhaul; fuel filter replacement; fuel tank and line inspection.
Ignition System:
Spark plug specifications, ignition coil testing, CDI unit diagnostics, and timing.
Cooling System:
Likely air-cooled, focusing on cylinder head and barrel heat dissipation; oil cooling if applicable.
Transmission Drivetrain:
CVT (Continuously Variable Transmission) belt inspection and replacement, clutch and variator service, final drive (gearbox) oil and maintenance.
Suspension:
Front fork overhaul, rear shock absorber inspection and replacement, linkage lubrication.
Brakes:
Front and rear brake system inspection, pad replacement, caliper service, brake fluid bleeding and replacement, drum brake adjustment (if applicable).
Electrical System:
Wiring diagrams, battery testing and maintenance, lighting system troubleshooting, starter motor operation, charging system (stator, rectifier/regulator).
Chassis Frame:
Frame inspection, steering bearing service, wheel bearing maintenance.
Bodywork Trim:
Panel removal and installation, seat maintenance, storage compartment access.
Routine Maintenance:
Oil changes, filter replacements, spark plug checks, tire pressure, chain/belt adjustment (if applicable).
Troubleshooting Guides:
Diagnostic procedures for common starting, running, and electrical issues.
Component Rebuilds:
Detailed steps for rebuilding engine components, carburetors, brake calipers, and suspension units.
Torque Specifications:
Precise torque values for all critical fasteners during assembly and disassembly.
Tightening Sequences:
Correct order for tightening cylinder head bolts, wheels, and other critical components.
Special Tool Identification:
Identification and usage of specialized tools required for specific repair procedures.
Depth:
Comprehensive, covering everything from basic maintenance to full engine and transmission rebuilds, including electrical diagnostics.
Engine Type:
4-stroke, SOHC, 2-valve, air-cooled
Displacement:
125cc (approx. 124.9 cc)
Bore X Stroke:
Typically around 52.0 mm x 58.0 mm (refer to manual for exact specifications)
Compression Ratio:
Typically around 10.0:1 to 11.0:1 (refer to manual for exact specifications)
Horsepower:
Approx. 10-12 PS (7.4-8.8 kW) at around 7,500-8,000 rpm (refer to manual for exact specifications)
Torque:
Approx. 9-10 Nm (6.6-7.4 lb-ft) at around 6,000-7,000 rpm (refer to manual for exact specifications)
Fuel Delivery:
Carburetor (likely a VM series or similar, e.g., VM24SH or Mikuni equivalent)
Carburetor Specifications:
Specific carburetor model, jet sizes (main, pilot), needle settings, float level, and idle speed are detailed in the manual.
Oil Type:
Yamalube (or equivalent SAE 10W-40 API SE, SF, SG, SH, SJ or higher motor oil)
Oil Capacity:
Approx. 0.8 - 1.0 liters (refer to manual for exact capacity with filter change)
Type:
Automatic CVT (Continuously Variable Transmission)
Drive Belt:
Specific V-belt dimensions, wear limits, and replacement intervals.
Variator Clutch:
Service and inspection of variator weights, drive face, torque driver, and clutch shoes.
Gear Reduction:
Final gear reduction ratios are specified for maintenance and troubleshooting.
Length:
Approx. 1,850 mm - 1,950 mm (refer to manual for exact specifications)
Width:
Approx. 700 mm - 750 mm (refer to manual for exact specifications)
Height:
Approx. 1,100 mm - 1,150 mm (refer to manual for exact specifications)
Wheelbase:
Approx. 1,300 mm - 1,350 mm (refer to manual for exact specifications)
Dry Weight:
Approx. 110 kg - 120 kg (refer to manual for exact specifications)
Fuel Tank Capacity:
Approx. 6.0 - 7.0 Liters (refer to manual for exact specifications)
Front Tire Size:
Typically 110/70-12 or 100/80-12 (refer to manual for exact specifications)
Rear Tire Size:
Typically 120/70-12 or 110/80-12 (refer to manual for exact specifications)
Wheel Type:
Typically cast aluminum alloy wheels
Safety Standards:
Complies with relevant road safety and emissions standards for its market of sale.
Braking System:
Disc front brake, Drum or Disc rear brake (check specific model variant); linked braking system might be present.
Lighting:
Halogen headlight, LED taillight (common in newer models, may vary), turn signals.
Frame Construction:
Steel underbone frame for rigidity and rider protection.
Instrument Cluster:
Analog speedometer, odometer, fuel gauge, and indicator lights for turn signals, high beam, and oil level/check engine (basic function).
ABS:
ABS was generally not a standard feature on 125cc scooters of this era, but it's always worth checking specific market variants; the manual would cover braking system specifics.
Smart Features:
No advanced smart features or connectivity expected for this model year.
Engine Oil Change:
Every 3,000 km or 6 months, whichever comes first (typical for Yamaha 125cc scooters, refer to manual for exact interval).
Air Filter Cleaning:
Every 3,000 km, replace as needed.
Spark Plug Check:
Every 5,000 km, replace as needed.
Cvt Belt Inspection:
Every 10,000 km, inspect for wear and damage, replace as needed.
Brake Pad Inspection:
Every 5,000 km, check for wear and replace as needed.
Engine Oil Spec:
SAE 10W-40 API SE, SF, SG, SH, SJ or higher.
Brake Fluid Spec:
DOT 3 or DOT 4 hydraulic brake fluid (refer to manual for exact specification).
Final Drive Gear Oil:
Yamaha Gear Oil (or equivalent SAE 80 API GL-4 hypoid gear oil).
Common Issues:
Typical issues may include carburetor clogging due to infrequent use, wear on CVT components (belt, rollers, clutch), aging electrical connections, and potential fork seal leaks. The manual addresses these with specific diagnostic and repair procedures.
Heritage:
Yamaha's long history in motorcycle and scooter manufacturing, known for reliability and performance innovations.
Evolution:
The YJ125S likely evolved from earlier Yamaha scooter designs, incorporating advancements in engine technology, ergonomics, and styling to meet market demands for efficient urban mobility.
Manufacturing Location:
Likely manufactured in Yamaha's facilities in Southeast Asia (e.g., Indonesia, Thailand, Vietnam) or Japan.
