🏷️ Basic Information

Make:

Yamaha

Model:

YZ 125

Product Type:

Workshop Service Manual

👋 Introduction

Vehicle Segment:

Competition Motocross / Off-Road Motorcycle

Key Competitors:

Honda CR125R, Kawasaki KX125, Suzuki RM125, KTM 125 EXC.

Target Audience:

Motocross racers, off-road enthusiasts, mechanics, and DIY owners seeking to maintain and repair their YZ 125.

Manual Benefit:

Empowers owners and technicians with comprehensive knowledge to perform all necessary maintenance and repairs, ensuring optimal performance and longevity of the YZ 125.

📋 Manual Details

Applicable Years:

1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006

Page Count:

553

Manual Type:

Service Manual / Repair Manual

Language:

English

Format:

PDF

📖 Manual Coverage

Engine Systems:

Top End (Cylinder, Piston, Rings), Bottom End (Crankshaft, Connecting Rod, Bearings), Carburetion, Ignition System, Cooling System (if applicable, though YZ125 is typically air-cooled in these years), Exhaust System.

Drivetrain Systems:

Clutch Assembly, Transmission (Gearbox), Shifting Mechanism, Drive Chain and Sprockets.

Chassis Systems:

Front Suspension (Fork), Rear Suspension (Monoshock), Frame, Swingarm, Steering System, Wheel Hubs.

Braking Systems:

Front Brake System (Caliper, Master Cylinder, Disc), Rear Brake System (Caliper, Master Cylinder, Disc).

Electrical Systems:

Ignition Coil, CDI Unit, Spark Plug, Wiring Harness, Lighting (if applicable), Fuses.

Maintenance Procedures:

Scheduled Maintenance (e.g., oil changes, filter cleaning), Air Filter Service, Spark Plug Replacement, Chain Adjustment and Lubrication, Brake Pad Inspection and Replacement, Suspension Service.

Repair Procedures:

Engine Overhaul (Top and Bottom End), Carburetor Rebuild, Clutch Replacement, Transmission Disassembly and Reassembly, Suspension Fork Rebuild, Shock Absorber Service, Brake System Bleeding and Component Replacement.

Troubleshooting Guides:

Diagnostic procedures for common performance issues, starting problems, electrical faults, and mechanical failures.

Diagnostic Capabilities:

Detailed fault finding charts and explanations of symptoms to identify root causes.

Rebuild Specifications:

Complete disassembly and reassembly instructions for all major components with precise torque specifications, clearances, and tolerances.

Adjustment Procedures:

Comprehensive instructions for adjusting carburetor settings, clutch engagement, throttle cable, and suspension pre-load.

📊 Manual Specifications

File Type:

Portable Document Format (PDF)

Searchability:

Text searchable for quick information retrieval.

Image Resolution:

High-resolution diagrams and illustrations for clarity.

Binding Type:

Not Applicable (Digital Download)

Paper Type:

Not Applicable (Digital Download)

⚙️ Engine Specifications

Engine Type:

2-stroke, Liquid-Cooled (later models) / Air-Cooled (early models), Single Cylinder

Displacement:

123cc (approximate, may vary slightly by year)

Bore X Stroke:

Typically 54.0 mm x 54.5 mm (check specific year for exact values)

Horsepower Range:

Approximately 35-40 HP (varies by year and tuning)

Torque Range:

Approximately 18-20 lb-ft (varies by year)

Fuel Delivery:

Carburetor (e.g., Mikuni VM series)

Carburetor Size:

Typically 34mm or 36mm

Ignition Type:

CDI (Capacitor Discharge Ignition)

🔧 Transmission

Transmission Type:

6-speed constant mesh manual

Clutch Type:

Wet, multi-plate

Gear Ratios:

Detailed in manual; specific ratios vary by year but are optimized for motocross performance.

📐 Dimensions

Dry Weight:

Approximately 90-95 kg (200-210 lbs) depending on year and specific components.

Fuel Capacity:

Approximately 8.0 liters (2.1 gallons)

Oil Capacity Transmission:

Approximately 0.7-1.0 liters (check manual for exact specification and type)

🛡️ Safety Features

Safety Standard:

N/A (Off-road vehicle, not subject to street-legal safety ratings)

Braking System Type:

Hydraulic disc brakes, front and rear.

Frame Construction:

Steel perimeter frame, designed for rigidity and durability.

💡 Technology Features

Infotainment System:

N/A (Pure performance off-road motorcycle, no infotainment features).

Assistance Features:

N/A (No electronic driver assistance features).

Connectivity Options:

N/A (No connectivity features).

🔧 Maintenance

Engine Top End Rebuild:

Recommended every 30-50 hours of aggressive riding (check manual for specific conditions).

Air Filter Cleaning:

Every few rides or as needed based on conditions.

Transmission Oil Change:

Every 10-20 hours of riding.

Transmission Oil Type:

Yamalube 10W-40 API SG or equivalent motorcycle-specific transmission oil (consult manual for exact API rating and viscosity).

Coolant Type:

If liquid-cooled: High-quality ethylene glycol-based coolant, mixed 50/50 with distilled water. (Check manual for specific Yamaha coolant recommendations).

Brake Fluid Type:

DOT 3 or DOT 4 Hydraulic Brake Fluid (consult manual for specific recommendation).

Common Wear Items:

Piston rings, clutch plates, wheel bearings, steering bearings, swingarm bushings, fork seals, brake pads.

Engine Issues:

Potential for scoring on cylinder walls and piston due to heat and wear, clutch slipping if not adjusted or replaced, kickstart mechanism wear.

Suspension Issues:

Fork seal leaks, shock absorber seal leaks, worn bushings leading to play.

Carburetor Issues:

Pilot jet clogging, main jet wear, float bowl issues affecting fuel mixture.

Air Filter Pnum Example:

Example: 1LX-14451-00-00 (Note: Part numbers vary by year, refer to the manual or parts fiche).

Oil Filter Pnum Example:

N/A (Typically no oil filter on 2-stroke engines, relies on transmission oil for lubrication).

📚 Vehicle History

Yamaha Motorsport Legacy:

Yamaha has a long and successful history in motorcycle racing, particularly in motocross, with the YZ line being a cornerstone of their off-road performance.

Yz125 Development:

The YZ 125 underwent significant updates throughout this period, including advancements in suspension technology (e.g., Kayaba components), engine performance (e.g., reed valve systems, exhaust port timing), chassis design, and braking systems, reflecting Yamaha's commitment to competition.

Production Period:

1986-2006

🏆 Awards & Recognition

Motocross Performance Awards:

The YZ 125 has consistently been lauded in motorcycle press for its class-leading performance, handling, and engine power throughout its production run, securing numerous 'Bike of the Year' or 'Best in Class' awards in its segment.

Rider Satisfaction:

High rider satisfaction due to its potent engine, agile chassis, and reliable performance in competitive motocross environments.