Segment:
Motocross / Off-Road Competition
Target User:
Enthusiasts, mechanics, racers seeking to maintain and repair their YZ125
Key Competitors:
KTM 125 SX, Honda CR125R, Suzuki RM125, Kawasaki KX125
Manual Value:
Authoritative guide for efficient and correct maintenance and repair
Vehicle Attributes:
Renowned for its agile handling and potent two-stroke power
Engine:
Top end, bottom end, lubrication, cooling, fuel system, ignition system, exhaust system
Transmission:
Clutch, gearbox, gear shift mechanism
Chassis:
Frame, suspension (front and rear), steering, wheels, tires, brakes, swingarm
Electrical:
Ignition system components, lighting, wiring diagrams, charging system (if applicable)
Maintenance:
Oil changes, filter replacement, chain adjustment, spark plug replacement, air filter cleaning
Repair:
Engine overhaul, carburetor rebuild, suspension service, brake bleeding, clutch service
Troubleshooting:
Diagnostic procedures for common faults, electrical diagnostics, engine performance issues
Specifications:
Torque values, clearances, fluid capacities, electrical specifications
Depth:
Comprehensive; covers basic maintenance to complete engine rebuilds and advanced diagnostics
Type:
Liquid-cooled, 2-stroke, Reed valve induction
Displacement:
124cc (7.57 cu. in.)
Bore X Stroke:
54 mm x 54.5 mm (2.13 in x 2.15 in)
Compression Ratio:
8.2:1 (approx.)
Horsepower Estimated:
35-40 HP (at crankshaft, approximate)
Torque Estimated:
17-19 lb-ft (at crankshaft, approximate)
Carburetor:
Keihin PWK38S (38mm) flat slide
Fuel Type:
Unleaded gasoline (90 octane or higher recommended)
Fuel Mixture:
50:1 ratio with premium 2-stroke oil
System:
Yamaha Autolube (Premix)
Coolant Capacity:
0.62 L (0.66 US qt)
Type:
Digital CDI (Capacitor Discharge Ignition)
Type:
6-speed constant mesh
Clutch:
Wet, multiple-disc
Gear Ratios:
1st: 2.833, 2nd: 2.063, 3rd: 1.571, 4th: 1.250, 5th: 1.042, 6th: 0.917 (specific ratios available in manual)
Transmission Oil Type:
Yamalube 2-stroke oil or equivalent (for Autolube system)
Oil Change Frequency:
Every 10-15 hours of riding, or as per manual recommendations
Air Filter Cleaning:
After every ride or as needed based on conditions
Spark Plug Replacement:
Every 20-30 hours of riding
Top End Rebuild:
100-150 hours (depending on riding style and maintenance)
Engine Oil:
Yamalube 2-stroke oil or equivalent (specific API grade recommended in manual)
Transmission Oil:
Yamalube Gear Oil or equivalent (specific viscosity recommended in manual, typically 10W-30)
Coolant:
Yamaha High Performance Coolant or a 50/50 mix of ethylene glycol-based antifreeze and distilled water
Brake Fluid:
DOT 3 or DOT 4 brake fluid
Common Wear Items:
Clutch plates, piston rings, air filter, spark plug, wheel bearings, steering bearings
Performance Tips:
Proper carburetor jetting and air-fuel mixture are critical for optimal performance and engine longevity.
Carburetor Maintenance:
Regular cleaning and inspection of the Keihin PWK carburetor is essential to prevent fuel delivery issues.
Yamaha Legacy:
Yamaha has a long-standing history of producing high-performance motocross bikes, dating back to the early days of the sport.
Yz125 Lineage:
The YZ125 has been a staple in Yamaha's lineup, consistently evolving to incorporate advanced technology and performance enhancements for motocross racing.
2002 Model Updates:
The 2002 model saw refinements in suspension, engine tuning, and chassis geometry for improved handling and responsiveness.
Manufacturing Location:
Japan
Motocross Performance:
The YZ125 platform has historically been a competitive force in amateur and professional motocross racing.
Owner Satisfaction:
Generally high, known for reliability and performance within its class.
Emissions:
N/A (Designed for closed-course competition, not street-legal)
