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Yamaha YZ125 2021 User Manual

Yamaha YZ125 2021
268 pages
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Read this manual carefully before operating this vehicle.
2021
OWNER’S SERVICE MANUAL
YZ125
YZ125M2
LIT-11626-34-27 B0V-2819U-10

Table of Contents

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Yamaha YZ125 2021 Specifications

General IconGeneral
Displacement125cc
Bore x Stroke54.0mm x 54.5mm
IgnitionCDI
Final DriveChain
Suspension FrontKYB® Speed-Sensitive System inverted fork; fully adjustable, 11.8-in travel
Brakes FrontHydraulic disc, 270mm
Brakes RearHydraulic disc, 240mm
Tires Front80/100-21
Tires Rear100/90-19
Engine TypeLiquid-cooled 2-stroke
Transmission6-speed
Suspension RearKYB® single shock; 12.4-in travel
Seat Height38.6 in
Compression Ratio8.6 - 10.7:1
Fuel DeliveryKeihin PWK38S carburetor

Summary

General Information

Safety Information

Essential safety guidelines for operating the vehicle, including riding practices and protective apparel.

Description

Illustrations and labels identifying key components and controls of the motorcycle.

Special Tools

List of special tools required for accurate adjustment and assembly, with part numbers.

Instrument and Control Functions

Explanation of the function and location of all instruments and controls on the motorcycle.

Starting and Break-In

Procedures for starting the engine, including cold and warm starts, and essential break-in guidelines.

Specifications

General Specifications

Provides basic dimensions, weight, and riding capacity of the motorcycle.

Engine Specifications

Detailed technical specifications for the engine, including displacement, bore, stroke, and fuel.

Chassis Specifications

Technical specifications for the chassis, including wheels, tires, brakes, and suspension.

Tightening Torques

Specifies general and specific tightening torques for fasteners to ensure proper assembly.

Periodic Checks and Adjustments

Maintenance Intervals

Defines recommended maintenance intervals for various parts and systems based on usage.

Pre-Operation Inspection and Maintenance

Checklist of pre-operation inspections and general maintenance required before riding.

Engine

Procedures for checking and adjusting engine components like pilot air screw and idle speed.

Chassis

Procedures for checking and adjusting chassis components like brakes, steering, and suspension.

Chassis

Front Wheel

Detailed steps for removing, disassembling, checking, and assembling the front wheel.

Rear Wheel

Detailed steps for removing, disassembling, checking, and assembling the rear wheel.

Front Brake

Procedures for removing, disassembling, checking, and installing the front brake system.

Rear Brake

Procedures for removing, disassembling, checking, and installing the rear brake system.

Front Fork

Detailed procedures for removing, disassembling, checking, and assembling the front fork legs.

Engine

Engine Removal

Detailed steps for removing the exhaust pipe and the engine assembly from the chassis.

Cylinder Head, Cylinder and Piston

Procedures for removing and checking cylinder head, cylinder, piston, and related parts.

Clutch

Procedures for removing, checking, and installing the clutch assembly and its components.

Crankshaft

Steps for removing, checking, and installing the crankshaft assembly.

Cooling System

Radiator

Procedures for removing and installing the radiator, and checking its condition.

Water Pump

Steps for disassembling, checking, and assembling the water pump.

Fuel System

Fuel Tank

Instructions for removing and installing the fuel tank and its related components.

Air Filter

Procedures for removing and installing the air filter element and case.

Carburetor

Detailed steps for removing, disassembling, checking, and installing the carburetor.

Electrical System

Wiring Diagram

Diagram illustrating the electrical connections and color codes for the entire system.

Ignition System

Troubleshooting guide for ignition system failures, including spark plug and coil checks.

Electrical Components

Illustrations and identification of major electrical components like CDI unit and ignition coil.

Troubleshooting

General Information

General guidelines and tips for performing basic troubleshooting on the vehicle.

Troubleshooting of Engine

Diagnosing and resolving engine starting or running issues, including fuel and spark problems.

Troubleshooting of Brake

Diagnosing and resolving poor disc brake performance or fluid leaks.

Troubleshooting of Suspension

Troubleshooting front and rear suspension stiffness, softness, or oil leaks.

Tuning

Carburetor Setting

Adjusting carburetor settings like main jet, pilot air screw, and pilot jet for optimal performance.

Road Condition and Examples of Carburetor Setting

Guidance on carburetor settings based on road conditions and common symptoms.

Front Fork Setting

Adjusting front fork settings for air spring, spring preload, and damping force.

Rear Suspension Setting

Adjusting rear suspension settings for spring preload and damping force.

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