Segment:
Performance-oriented 125cc two-stroke motocross motorcycle.
Target Audience:
Motocross racers, enthusiasts, and mechanics seeking to maintain and repair the YZ125.
Key Competitors:
KTM 125 SX, Honda CR125R, Suzuki RM125, Kawasaki KX125.
Yz125 Heritage:
The YZ125 is a long-standing and highly regarded model in the motocross world, known for its potent two-stroke power and agile handling.
Manual Value Proposition:
Provides the essential information required for proper maintenance, repair, and optimization of the 2005 YZ125, enabling owners to keep their bikes performing at their peak.
General Coverage:
Comprehensive service and repair for the 2005 Yamaha YZ125
Specific Systems Covered:
Engine, fuel system, ignition system, transmission, clutch, suspension (front and rear), brakes (front and rear), chassis, electrical system, cooling system, lubrication system
Estimated Pages:
Likely 300-500 pages (typical for a full service manual)
Type:
Service Repair Workshop Manual
Format:
Digital Download (PDF)
Engine Overhaul:
Complete disassembly, inspection, repair, and reassembly procedures for the YZ125's 2-stroke engine.
Carburetion:
Detailed information on the Keihin carburetor, including jetting, adjustments, and overhaul.
Transmission Clutch:
Procedures for clutch maintenance, replacement, and transmission disassembly/reassembly.
Suspension Forks:
Service and tuning information for the front KYB (Kayaba) SSS (Speed Sensitive System) forks or similar, including fluid levels and seal replacement.
Suspension Shock:
Maintenance and adjustments for the rear KYB shock absorber, including linkage service.
Brakes:
Front and rear brake system maintenance, including hydraulic fluid changes, caliper service, and pad replacement.
Electrical:
Wiring diagrams, troubleshooting for the ignition and lighting systems (if applicable).
Scheduled Maintenance:
Oil changes, filter cleaning/replacement, spark plug service, chain adjustment, and lubrication.
Troubleshooting:
Diagnostic procedures for common problems, with symptom-based troubleshooting guides.
Component Repair:
Step-by-step instructions for repairing or replacing individual components within all major systems.
Rebuild Procedures:
Detailed instructions for engine top-end rebuilds and potential bottom-end work.
Torque Specifications:
Precise torque values for all critical fasteners and bolts.
Depth:
Comprehensive, covering from basic rider maintenance to complete engine and chassis rebuilds.
Diagnostic Capabilities:
Includes troubleshooting charts and information to diagnose mechanical and electrical issues.
Specifications Accuracy:
Highly accurate, based on Yamaha's factory specifications for the 2005 YZ125 model.
Engine Type:
Liquid-cooled, 2-stroke, reed valve, YPVS (Yamaha Power Valve System)
Bore X Stroke:
54.0 mm x 54.5 mm
Compression Ratio:
8.6:1 (at constant volume)
Carburetor:
Keihin PWK38S, 1x Flat slide
Horsepower:
Approximately 35-40 HP (estimated at crank, actual varies)
Torque:
Not readily available in public domain, but characteristic of a strong mid-range for its class.
Fuel Type:
Unleaded gasoline, minimum 91 octane (RON+MON)/2
Fuel Mixture:
Requires 2-stroke engine oil pre-mixed with gasoline (ratio specified in manual, typically 32:1 or 40:1).
Fuel Tank Capacity:
8.0 Liters (2.1 US gal)
Safety Ratings:
N/A (Motocross motorcycles are not subject to standard automotive safety ratings).
Braking System:
Hydraulic disc brakes front and rear for effective stopping power.
Suspension Performance:
High-quality suspension contributes to rider control and stability.
Chassis Design:
Rigid and well-balanced chassis for predictable handling.
Features:
N/A (Motocross motorcycle, no infotainment features).
Features:
N/A (No electronic rider aids).
Features:
N/A (No connectivity features).
Ypvs:
Yamaha Power Valve System (YPVS) for improved power delivery across the rev range.
Oil Change Engine:
As per manual, typically every 10-15 hours of riding or annually.
Air Filter Cleaning:
Frequent cleaning recommended, especially in dusty conditions (e.g., after every few hours of riding).
Spark Plug Replacement:
Check and clean periodically, replace as needed based on condition (manual will specify).
Chain Lubrication Adjustment:
Lubricate before every ride, adjust chain slack as per manual specifications.
Engine Oil:
Yamalube 2-stroke oil or equivalent meeting JASO FD, API TC specifications. Mixture ratio specified in manual (e.g., 32:1 or 40:1).
Transmission Oil:
Yamalube Hypoid Gear Oil SAE 80W or equivalent.
Coolant:
High-quality permanent type antifreeze/coolant with a 50/50 mix of ethylene glycol and distilled water.
Brake Fluid:
DOT 4 hydraulic brake fluid.
Common Wear Items:
Piston rings, clutch plates, spark plugs, and chain/sprockets are typical wear items on high-performance 2-strokes.
Suspension Seals:
Fork and shock seal leaks can occur with heavy use and require regular inspection and maintenance.
Ypvs System:
The Yamaha Power Valve System (YPVS) can accumulate carbon and require periodic cleaning to maintain optimal performance.
General Reputation:
The YZ125 has consistently received praise from riders and media for its performance and handling characteristics throughout its production run.
Rider Reviews:
Highly rated by enthusiasts for its fun factor, lightweight chassis, and potent 2-stroke engine.
Standards:
Manufactured to Yamaha's high-quality standards and industry regulations for off-road vehicles.
