Market Segment:
Entry-level to intermediate motocross racing and aggressive off-road riding
Competitors:
Honda CR125R, Kawasaki KX125, Suzuki RM125, KTM 125 EXC
Engine Type:
High-performance liquid-cooled 125cc two-stroke
Suspension:
Advanced adjustable front forks and rear monoshock suspension for optimal off-road performance
Chassis:
Lightweight and durable chassis designed for agility and handling
Utility:
Essential for owners to perform regular maintenance, repairs, and troubleshooting, ensuring optimal performance and longevity of the competition machine.
Engine Overhaul:
Complete disassembly, inspection, reassembly of the two-stroke engine
Cooling System:
Radiator, hoses, water pump maintenance and repair (if applicable to YZ125 of this generation, typically liquid-cooled)
Fuel System:
Carburetor tuning, cleaning, rebuilding; fuel tank, petcock, fuel lines
Ignition System:
CDI, ignition coil, spark plug specifications, troubleshooting
Exhaust System:
Pipe, silencer maintenance and repair
Transmission And Drivetrain:
Clutch operation, gear shifting mechanism, chain and sprocket maintenance
Suspension Front:
Fork disassembly, seal replacement, oil levels, damping adjustments
Suspension Rear:
Monoshock linkage, shock absorber service, spring adjustments
Brakes Front:
Hydraulic disc brake system, caliper, master cylinder, rotor maintenance
Brakes Rear:
Hydraulic disc brake system, caliper, master cylinder, rotor maintenance
Wheel And Tire:
Wheel bearing service, spoke tensioning, tire installation
Electrical System:
Wiring diagrams, lighting, battery maintenance (minimal on competition bikes)
Chassis And Frame:
Frame inspection, steering head bearing service
Bodywork And Plastics:
Fairing, seat, fenders removal and installation
Routine Maintenance:
Oil changes, filter cleaning/replacement, chain lubrication and adjustment, spark plug checks
Troubleshooting Guides:
Diagnostic flowcharts for common performance issues
Component Disassembly And Assembly:
Detailed step-by-step instructions for all major components
Rebuilding Procedures:
Engine top-end rebuild, carburetor rebuild, suspension seal replacement
Torque Specifications:
Precise torque values for critical fasteners
Wiring Diagrams:
Comprehensive electrical schematics for fault finding
Special Tools:
Identification of necessary specialized tools for specific procedures
Depth:
Comprehensive (from basic maintenance to full engine rebuilds and detailed diagnostics)
Engine Type:
Liquid-cooled, 2-stroke, Reed valve, Case-reed induction
Bore X Stroke:
54.0 mm x 54.5 mm (approximate, to be confirmed by manual)
Compression Ratio:
8.8:1 (typical for the era, verify in manual)
Horsepower:
Approx. 33-36 HP at ~11,500 RPM (typical for this model, verify in manual)
Torque:
Approx. 17-18 lb-ft at ~10,000 RPM (typical, verify in manual)
Carburetor:
Mikuni VM28SS (common for this model, verify in manual)
Fuel Type:
Unleaded gasoline (pre-mix with 2-stroke oil)
Premix Ratio:
50:1 or 40:1 (depending on oil and conditions, consult manual)
Ignition System:
CDI (Capacitor Discharge Ignition)
Length:
Approx. 2170 mm / 85.4 in (verify in manual)
Width:
Approx. 830 mm / 32.7 in (verify in manual)
Height:
Approx. 1265 mm / 49.8 in (verify in manual)
Dry Weight:
Approx. 93 kg / 205 lbs (verify in manual)
Fuel Tank Capacity:
Approx. 8.0 liters / 2.1 gallons (verify in manual)
Wheelbase:
Approx. 1475 mm / 58.1 in (verify in manual)
Ground Clearance:
Approx. 340 mm / 13.4 in (verify in manual)
Infotainment System:
N/A (Competition off-road motorcycle, no infotainment system)
Driver Assistance:
N/A (Competition off-road motorcycle, no driver assistance features)
Connectivity:
N/A (Competition off-road motorcycle, no connectivity features)
Engine Management:
Basic electronic ignition (CDI) with mechanical power valve operation.
Oil Change:
Every 10-15 hours of operation or per competition schedule (verify in manual)
Air Filter Cleaning:
After every few rides or more frequently in dusty conditions (verify in manual)
Top End Rebuild:
Recommended every 40-60 hours of hard use (verify in manual)
Fork Oil Type:
Yamaha Genuine Fork Oil (e.g., 01 or 01A) or equivalent viscosity like SAE 5W/10W (verify in manual for specific weight and volume)
Coolant:
Permanent type antifreeze, 50/50 mixture with distilled water (verify in manual)
Transmission Oil:
Yamalube Gear Oil 10W-30 or equivalent API SE, SF class SAE 10W-30 (verify in manual for capacity)
Power Valve:
Carbon buildup on the power valve can affect performance, requiring regular cleaning and inspection.
Clutch Wear:
Clutch plates can wear relatively quickly with aggressive riding and require periodic replacement.
Suspension Seals:
Fork seals and shock seals are common wear items that can leak over time and require replacement.
Carburetor Jetting:
Proper carburetor jetting is crucial for optimal performance at different altitudes and temperatures.
Yamaha Legacy:
Yamaha has a long and storied history in dirt bike racing, particularly in the 125cc class, with consistent development and competitive machines.
Yz Series Evolution:
The YZ125 has been a staple for Yamaha, evolving from earlier air-cooled models to the liquid-cooled, performance-oriented machines of the 1990s. The 1997-1998 models represent a refinement of the chassis and engine performance from the mid-90s.
Production Period:
The YZ125 has been in continuous production for decades, with significant updates occurring throughout its lifespan.
Racing Success:
The YZ125 platform has a rich history of success in amateur and professional motocross and supercross racing worldwide.
Editorial Reviews:
Periodically reviewed by motorcycle publications for its handling, engine performance, and value in the 125cc class.
Emissions Standards:
N/A (Designed for off-road competition, not road-legal or subject to typical emissions certifications for street vehicles)
