Segment:
Competition Motocross
Target Audience:
Motocross racers, performance enthusiasts, mechanics
Key Competitors:
Honda CR125R, Kawasaki KX125, Suzuki RM125
Manual Advantage:
Original Yamaha documentation ensures accuracy and completeness for maintenance and repair.
Illustration Quality:
Illustrated with clear, detailed diagrams to aid understanding.
Instruction Style:
Step-by-step instructions facilitate both routine tasks and complex repairs.
Engine:
Complete disassembly, assembly, inspection, tuning, cooling system, lubrication system
Transmission:
Gearbox disassembly, assembly, inspection, clutch operation, shift mechanism
Chassis:
Frame, suspension (front forks, rear shock absorber), steering system, swingarm
Brakes:
Front and rear brake systems, hydraulic lines, caliper overhaul, brake fluid specifications
Electrical:
Ignition system, lighting, charging system, wiring diagrams, CDI unit, troubleshooting electrical faults
Fuel System:
Carburetor tuning and overhaul, fuel lines, fuel tank maintenance
Cooling System:
Radiator, coolant specifications, water pump maintenance (if applicable)
Exhaust System:
Exhaust pipe, silencer maintenance and inspection
Wheels And Tires:
Wheel bearing inspection, tire pressure specifications, spoke tensioning
Routine Maintenance:
Oil changes, filter replacements, chain adjustment, spark plug replacement, air filter cleaning
Engine Repair:
Top-end rebuild (piston, rings, cylinder), crankshaft and bearing replacement, valve adjustment (if applicable, though this is a 2-stroke)
Transmission Repair:
Complete gearbox disassembly and reassembly, clutch plate replacement
Suspension Adjustment:
Front fork oil change and seal replacement, rear shock absorber servicing and adjustment
Brake System Overhaul:
Caliper rebuild, master cylinder servicing, bleeding procedure
Electrical Troubleshooting:
Diagnosis of common electrical faults, component testing
Carburetor Tuning:
Jetting recommendations, idle speed adjustment, mixture screw settings
Wiring Diagram Interpretation:
Detailed schematics for all electrical circuits
Depth:
Comprehensive, suitable for professional mechanics and experienced DIY enthusiasts
Detail Level:
Illustrated with clear step-by-step instructions and detailed diagrams
Type:
2-stroke, single-cylinder
Bore X Stroke:
54.0 mm x 54.5 mm
Compression Ratio:
8.8:1 (approx.)
Cooling System:
Liquid-cooled
Ignition:
CDI (Capacitor Discharge Ignition)
Horsepower Estimated:
35-38 HP (at Crankshaft)
Torque Estimated:
18-20 lb-ft (at Crankshaft)
Carburetor Model:
Keihin PWK38 (typically)
Fuel Type:
Unleaded gasoline with 2-stroke oil premix
Premix Ratio:
50:1 (Yamaha recommended)
Oil Change Engine:
Every 10-15 hours of riding or annually, check level frequently.
Air Filter Cleaning:
After every few rides, depending on conditions.
Chain Adjustment:
Every 5-10 hours of riding.
Spark Plug Replacement:
Every 20-30 hours of riding or as needed based on inspection.
Top End Rebuild:
Every 40-60 hours of hard riding (piston, rings, cylinder inspection).
Engine Oil:
High-quality 2-stroke premix oil (e.g., Yamalube 2R or equivalent)
Transmission Oil:
Yamalube SAE 10W-30 API SG or API SH (check manual for exact spec, e.g., 0.65L capacity)
Coolant:
Permanent type coolant (ethylene glycol based), 50% solution with distilled water (approx. 1.5L capacity)
Brake Fluid:
DOT 3 or DOT 4 hydraulic brake fluid
Power Valve Sticking:
Carbon buildup can cause the power valve to stick, leading to performance loss. Requires periodic cleaning.
Clutch Slippage:
Aggressive riding or worn plates can lead to clutch slippage. Regular inspection and replacement are necessary.
Suspension Seals:
Front fork seals can wear over time, leading to oil leaks. Regular inspection and replacement are recommended.
Carburetor Jetting:
Stock jetting may need adjustment based on altitude, temperature, and modifications for optimal performance.
