Market Segment:
Performance Motocross / Off-Road Competition
Competitors:
KTM 125 SX, Honda CR125R (discontinued prior to 2008, but relevant history), Kawasaki KX125 (discontinued prior to 2008), Suzuki RM125 (discontinued prior to 2008).
Yz125 Reputation:
Renowned for its agile handling, powerful engine for its class, and competitive performance in motocross racing.
Manual Value:
Essential resource for owners and mechanics to maintain, repair, and optimize the performance of the 2008 YZ125.
Coverage:
Complete teardown and rebuild, maintenance, troubleshooting, electrical system, engine, chassis, suspension, brakes, bodywork, specifications.
Manual Type:
Factory Service Manual / Repair Manual
Format:
Digital Download (PDF)
Engine:
2-stroke, liquid-cooled, reed valve induction, YPVS (Yamaha Power Valve System), carburetor, ignition system, cooling system.
Transmission:
6-speed sequential, clutch system, lubrication.
Chassis:
Frame construction (aluminum twin-spar), sub-frame, steering system, swingarm.
Suspension:
Front: Inverted telescopic fork (Kayaba Speed Sensitive System - SSS), Rear: Monocross suspension with adjustable shock absorber (Kayaba).
Brakes:
Front: Hydraulic disc brake with dual-piston caliper, Rear: Hydraulic disc brake with single-piston caliper.
Electrical:
CDI ignition system, lighting (if applicable for specific variants), wiring diagrams.
Fuel System:
Fuel tank capacity, fuel delivery system, carburetor settings (Keihin PWK38S).
Bodywork:
Plastics, seat, handlebars, footpegs.
Routine Maintenance:
Air filter cleaning/replacement, spark plug inspection/replacement, chain adjustment/lubrication, oil changes (transmission), general inspection.
Engine Overhaul:
Complete engine disassembly, piston and ring replacement, cylinder inspection/honing, crankshaft and bearing service, clutch service, YPVS system maintenance.
Suspension Service:
Fork seal replacement, fork oil change and level adjustment, rear shock absorber service and adjustments.
Brake Service:
Brake pad replacement, brake fluid flush and replacement, caliper inspection and service.
Troubleshooting:
Diagnostic procedures for common running issues, electrical system faults, starting problems.
Torque Specifications:
Detailed torque values for all critical fasteners.
Depth:
Comprehensive. Covers basic maintenance to complete engine and chassis rebuilds with detailed diagrams and step-by-step instructions.
File Format:
PDF (Portable Document Format)
Print Quality:
High-resolution scans of original factory documentation, ensuring clarity of text and diagrams.
Binding Type:
N/A (Digital Download)
Paper Type:
N/A (Digital Download)
Searchability:
Likely searchable text within the PDF, allowing for quick access to specific topics.
Illustrations:
Includes detailed pictures, line drawings, and part diagrams.
Engine Type:
2-stroke, single-cylinder
Bore X Stroke:
54 mm x 54.5 mm
Cooling System:
Liquid-cooled
Valve System:
Reed valve induction with YPVS (Yamaha Power Valve System)
Horsepower:
Approximately 35-40 HP (peak, estimate based on class for the era)
Torque:
Approximately 17-19 lb-ft (peak, estimate based on class for the era)
Carburetor:
Keihin PWK38S, single
Fuel Type:
Unleaded gasoline (91 octane or higher recommended)
Fuel Oil Mixture:
50:1 ratio of unleaded gasoline to 2-stroke oil (specific Yamalube recommended)
Transmission Type:
6-speed, constant mesh, sequential
Clutch:
Wet, multi-plate, cable-operated
Gear Ratios:
Specific gear ratios will be detailed within the manual, crucial for performance tuning.
Transmission Oil Type:
Yamaha genuine gear oil (e.g., Yamalube 10W-40 or equivalent API GL-4 specification)
Transmission Oil Capacity:
Approximately 0.75 liters (check manual for exact capacity and fill procedure)
Safety Standards:
Designed for off-road competition; no road-legal safety ratings (e.g., NHTSA, Euro NCAP) apply.
Braking System:
Powerful hydraulic disc brakes front and rear for effective stopping power.
Frame Design:
Durable aluminum twin-spar frame provides rigidity and crash protection for core components.
Infotainment Features:
N/A - Pure performance off-road motorcycle with no infotainment system.
Assistance Systems:
N/A - No electronic rider aids or driver assistance systems.
Connectivity Features:
N/A - No connectivity features.
Ypvs System:
Yamaha Power Valve System (YPVS) electronically controls exhaust port timing to optimize power delivery across the RPM range.
Engine Top End Rebuild:
Recommended every 20-40 hours of racing/hard use, depending on rider style and maintenance.
Transmission Oil Change:
Every 10-15 hours of use or after major events.
Air Filter Cleaning:
After every ride, or more frequently in dusty conditions.
Spark Plug Inspection:
Every 5-10 hours of use.
Cooling System Coolant:
High-quality engine coolant/antifreeze mixture (50:50 with distilled water) with anti-corrosive additives. Yamaha recommends Yamalube Coolant.
Brake Fluid Type:
DOT 4 Hydraulic Brake Fluid.
Clutch Wear:
Like many 2-stroke motocross bikes, the clutch can wear out with aggressive riding; regular inspection and adjustment are key.
Ypvs System:
Carbon buildup on the power valve can affect performance; requires periodic cleaning as per manual recommendations.
Suspension Maintenance:
Properly maintaining fork and shock oil levels and seal condition is crucial for optimal performance and longevity.
Yamaha Motorcycles:
Yamaha Motor Company has a long and successful history in motorcycle manufacturing, particularly in the off-road and racing segments.
Yz Series Development:
The YZ125 is a long-standing model within Yamaha's YZ motocross line, evolving significantly over decades with advancements in engine technology, suspension, and chassis design.
Yz125 Production Years:
The YZ125 has been in continuous production for many years, with significant updates in 2001 (new frame) and further refinements leading up to the 2008 model.
Motocross Awards:
While specific awards for the 2008 model might not be universally documented, the YZ125 has historically been praised in motorsport media for its performance and handling, often winning comparison tests within its class.
Editorial Reviews:
Reviews from motocross publications typically highlight the YZ125's strong engine, excellent chassis balance, and top-tier suspension (Kayaba SSS components).
