Segment:
Motocross / Off-Road Competition Motorcycle
Target Audience:
Motocross racers, off-road enthusiasts, mechanics
Key Competitors Era:
KTM 125 SX, Honda CR125R, Suzuki RM125, Kawasaki KX125
Yz125 Reputation:
Renowned for its potent 125cc two-stroke engine, nimble handling, and race-proven performance
Manual Utility:
Essential tool for maintaining peak performance, diagnosing issues, and performing complex repairs on the YZ125
Engine:
Top end, bottom end, lubrication, cooling, fuel, ignition, exhaust
Transmission:
Clutch, gearbox, shifting mechanism, drive chain
Chassis:
Frame, suspension (front forks, rear shock), steering, wheels, tires
Brakes:
Front and rear hydraulic disc brakes, fluid system
Electrical:
Ignition system, lighting (if applicable), wiring diagrams, CDI unit
Bodywork:
Plastics, seat, fuel tank, handlebars, controls
Maintenance:
Oil changes, filter replacement, chain adjustment, spark plug inspection/replacement, general inspections
Repair:
Engine rebuild (piston, rings, cylinder, crankshaft), transmission overhaul, suspension servicing, brake system repairs, carburetor tuning/rebuild
Troubleshooting:
Diagnosis of common mechanical and electrical issues, symptom-based troubleshooting guides
Specifications:
Torque values, clearances, fluid capacities, wear limits, electrical specifications
Depth:
Comprehensive, suitable for both amateur mechanics and professional technicians
Engine Type:
124cc liquid-cooled, 2-stroke, reed valve inducted, single-cylinder
Bore X Stroke:
54.0 mm x 54.5 mm
Compression Ratio:
8.1:1 (or similar, specific value in manual)
Carburetor:
Keihin PWK38S (38mm) with Power Jet
Horsepower Est:
Approximately 35-40 HP (at crank, depending on tuning)
Torque Est:
Approximately 18-20 lb-ft (at crank, depending on tuning)
Fuel Type:
Unleaded gasoline (91-98 octane recommended)
Fuel Mixture:
2-stroke oil mixed with fuel (typically 20:1 or 32:1, consult manual for exact ratio)
Oil Type:
Yamalube 2R or equivalent high-performance 2-stroke racing oil
Cooling System:
Liquid-cooled
Coolant Type:
Yamaha Super Coolant or equivalent antifreeze/water mixture (50/50)
Transmission Type:
6-speed constant mesh
Clutch Type:
Wet, multiple-disc
Gear Ratios:
Specific ratios detailed in manual (e.g., 1st: 2.333, 2nd: 1.750, 3rd: 1.333, 4th: 1.143, 5th: 1.000, 6th: 0.875)
Drive Chain Spec:
520 O-ring chain (recommend specific pitch/size from manual)
Safety Standards:
Designed for closed-course competition use only; not street legal
Braking System:
Hydraulic disc brakes front and rear for strong stopping power
Suspension Performance:
Adjustable front forks and rear shock for customizable handling and control
Frame Construction:
Durable aluminum frame for strength and lightweight chassis
Infotainment System:
N/A (Competition Off-Road Motorcycle)
Assistance Features:
N/A (Competition Off-Road Motorcycle)
Connectivity Features:
N/A (Competition Off-Road Motorcycle)
Power Valve System:
Yamaha's YPVS (Yamaha Power Valve System) for improved power delivery across the RPM range
Oil Change Interval:
Every 15-20 hours of use or as recommended by Yamaha
Air Filter Cleaning:
After every few rides, or more frequently in dusty conditions
Spark Plug Replacement:
Every 20-40 hours of use or when fouled
Chain Lubrication Adjustment:
Regularly, before each ride or every few hours of use
Top End Rebuild:
Every 60-100 hours of hard use (piston, rings, power valve service)
Transmission Oil Type:
Yamalube 10W-30 or equivalent SAE 10W-30 API SG, SF or SH transmission oil
Transmission Oil Capacity:
0.80 L (0.85 US qt)
Fork Oil Type:
Yamalube Fork Oil G10 or equivalent SAE 10W fork oil
Fork Oil Capacity Per Leg:
Specific volume detailed in manual (e.g., 0.50 L)
Common Wear Items:
Piston and rings, clutch plates, wheel bearings, steering head bearings, swingarm pivot bearings
Carburetor Tuning Sensitivity:
Can be sensitive to altitude and temperature changes, requiring re-jetting
Power Valve Maintenance:
Requires periodic cleaning and inspection to ensure proper function
Yamaha Legacy:
Yamaha has a long and storied history in motorcycle racing, particularly in motocross with its YZ series
Yz125 Development:
The YZ125 has been a staple in Yamaha's lineup for decades, continuously refined for performance and handling
2006 Updates:
The 2006 model saw refinements in suspension, engine tuning, and chassis improvements over previous years
Manufacturing Location:
Japan (typically)
