Segment:
Motocross Competition Motorcycle
Target Audience:
Motocross racers, off-road enthusiasts, and DIY mechanics.
Key Competitors:
Honda CR125R, Kawasaki KX125, Suzuki RM125, KTM 125 EXC.
Engine Type:
High-performance liquid-cooled two-stroke engine.
Suspension Type:
Advanced upside-down front forks and Monocross rear suspension.
Handling Characteristics:
Renowned for its lightweight chassis and agile handling.
Covered Years:
Primarily 2000, compatible with similar years (e.g., 1985 mentioned as an example, but focus is 2000 model range).
Page Count Estimate:
Estimated 400-500 pages (typical for a comprehensive service manual of this era).
Manual Type:
Service Repair Workshop Manual
Manual Completeness:
Complete factory service manual covering all aspects of the vehicle.
Format:
Likely Digital (PDF) given product description, with potential for print-on-demand.
Engine Service:
Complete engine disassembly, assembly, inspection, and repair procedures for the 125cc two-stroke engine.
Transmission Service:
Clutch, gearbox, shift mechanism, lubrication, and inspection procedures.
Cooling System:
Radiator, hoses, water pump, coolant specifications, and maintenance.
Fuel System:
Carburetor disassembly, cleaning, adjustment, jetting specifications, fuel tank, and fuel lines.
Ignition System:
CDI unit, spark plug specifications, ignition timing, stator, and coil testing.
Exhaust System:
Exhaust pipe, silencer inspection and maintenance.
Frame And Suspension:
Frame inspection, front fork (upside-down type) disassembly, service, and rear shock absorber maintenance.
Wheel And Tire:
Wheel bearing service, spoke tensioning, tire pressure specifications, and wheel removal/installation.
Brake System:
Front and rear hydraulic disc brake system service, including caliper, master cylinder, and fluid specifications.
Electrical System:
Wiring diagrams, lighting, horn, battery maintenance, and basic troubleshooting.
Bodywork And Controls:
Handlebar, levers, cables, seat, plastic body panels, and decal application.
Preventative Maintenance:
Detailed schedules and procedures for routine checks and servicing.
Troubleshooting Guides:
Systematic diagnostic procedures for common problems and malfunctions.
Rebuild Procedures:
Step-by-step instructions for complete engine, transmission, and suspension overhauls.
Adjustment Procedures:
Carburetor tuning, clutch adjustment, chain tensioning, and brake lever free play.
Torque Specifications:
Precise torque values for all critical fasteners and components.
Special Tool Requirements:
Identification and usage of specialized tools required for certain repairs.
Diagnostic Capabilities:
Advanced diagnostics for ignition, fuel, and engine performance issues.
Repair Level:
Covers everything from basic maintenance to complete engine rebuilds and frame repairs.
Wiring Diagrams Detail:
Comprehensive and detailed electrical wiring schematics.
Engine Type:
Liquid-cooled, 2-stroke, reed valve, single-cylinder
Bore X Stroke:
54 mm x 54.5 mm
Compression Ratio:
9.7:1 (typical for this model year)
Intake System:
Reed valve intake
Horsepower Estimate:
Approximately 35-40 hp (at crank)
Torque Estimate:
Approximately 18-20 lb-ft (at crank)
Carburetor Model:
Keihin PWK38 (typically)
Fuel Type:
Unleaded gasoline, minimum 91 octane (RON+MON)/2
Oil Mixing:
Pre-mix (2-stroke engine oil mixed with gasoline)
Transmission Oil Type:
Yamalube 2R or equivalent SAE 10W-30 API SE/SF/SG
Transmission Type:
Constant mesh 6-speed sequential
Clutch Type:
Wet, multi-disc, cable-actuated
Gear Ratios:
Refer to manual for specific ratios (e.g., 1st: 2.333, 2nd: 1.750, 3rd: 1.333, 4th: 1.090, 5th: 0.917, 6th: 0.750 - illustrative)
Oil Change Interval:
Refer to manual; typically every 10-15 hours of operation or annually.
Air Filter Cleaning:
Recommended after every few rides or when visibly dirty.
Spark Plug Replacement:
Refer to manual; typically every 20-30 hours of operation.
Top End Rebuild:
Recommended based on usage, often between 40-80 hours for competitive riding.
Coolant Type:
Yamaha Super Coolant or equivalent ethylene glycol-based coolant, 50/50 mix with distilled water.
Brake Fluid Type:
DOT 4 hydraulic brake fluid
Fork Oil Type:
Yamaha Fork Oil G10 or equivalent SAE 10W suspension fluid
Fork Oil Level:
Refer to manual for specific oil level (e.g., 135 mm from top of inner tube with spring removed)
Carburetor Tuning:
Can be sensitive to altitude and temperature; requires proper jetting for optimal performance.
Clutch Wear:
Clutch plates can wear over time, especially with aggressive riding; requires periodic adjustment and eventual replacement.
Suspension Seals:
Front fork and rear shock seals can leak with heavy use; regular inspection and maintenance are advised.
Heritage:
Yamaha has a long and successful history in motocross racing, with the YZ line being a cornerstone of their off-road performance.
Yz Line History:
The YZ125 has been a dominant force in the 125cc class for decades, known for continuous refinement and racing-focused development.
2000 Model Updates:
The 2000 model year saw significant updates including improved suspension, chassis geometry, and engine tuning, building on the success of previous generations.
Production Era:
The YZ125 has been in continuous production since the 1970s.
