1986 Yamaha YZ125S Service Manual

Service manual for Yamaha YZ125S models, covering engine, chassis, electrical, and maintenance procedures. Publication LIT-11626-05-13.

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Document Details

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Document Number / Seller:
26557 / Thomas Morgan
File Size:
18.45 MB
File Type:
ZIP
Language:
English
Printable:
Yes
Category:
Motorcycle
Last updated / verified
Jun 20, 2025

Models Covered & Key Technical Specifications

Unified Reference Shop Manual: Yamaha YZ125S (LIT-11626-05-13) 1986 Service Manual | Edition

  • Established Throughput Data: 25 ppm establishes the maximum print output Architecture.
  • Operational Angular Speed: For optimal function, 11,000 rpm defines the engine speed Framework.
  • Essential Package Size: 1.6 L -- signifies the active fuel tank capacity Threshold.
  • Baseline Moment Values: The transmission requires 8.1 - 10.5 : 1 for standard operation Logic.
  • Integral Fit Tolerances: Wheelbase reaches 1,450 mm Parameters.
  • Specific Speed Rating: The engine oil grade is specified as Yamalube "R" Norms.

Professional Workshop Service Manual & Technical Specifications

Unified Reference Shop Manual: Yamaha YZ125S (LIT-11626-05-13) : DL this manual (1986) Troubleshooting-Index

Engine-Type: Motorcycle // Model-Designation: YZ125S / Yamaha Motor Corp., Ltd // Engine-Type: 2-stroke Logic.

Document Overview

Integrated-Framework Diagnostic-Logic Logic
General Information Engine Maintenance and Repair Maintenance Intervals
Periodic Inspection and Adjustment Chassis Maintenance and Repair Lubrication
Electrical Appendices Technical Documentation

Repair data is categorized into sections covering general information, periodic maintenance and adjustments, engine repair, chassis repair, electrical systems, and appendices. This manual details various systems and procedures, including engine operation descriptions, assembly instructions for key components, and hydraulic schematics where applicable. It documents torque specifications for critical engine components to ensure proper dynamic load distribution.

System operation descriptions cover:

Engine components, fuel systems, and ignition timing.

The documentation addresses:

Carburetor assembly, maintenance, and adjustments, including pilot air screw and jet needle settings.

Assembly instructions are detailed for:

Crankcase, cylinder, and piston ring assembly, ensuring correct alignment and torque values.

Hydraulic schematics are included for:

Front and rear brake systems, including caliper and master cylinder disassembly.

Steering component information is provided for:

Steering head bearing inspection and adjustment, along with front fork servicing.

FAQ

What **documented** safety precautions are included regarding fuel handling? keyboard_arrow_down

1.98 US gal is the maximum fuel tank capacity; always turn the engine off before refueling and keep a rag handy for spills.

Confirm the **precise** lubrication requirements for the drive chain. keyboard_arrow_down

Chain slack should be maintained between 30 - 50 mm (1.2 - 2.0 in); use Yamaha cable lube or chain lube for application.

What tools are required for **proper** testing of ignition coils? keyboard_arrow_down

Primary Coil Resistance should be 0.22Ω ± 10% at 20°C (68°F), and Secondary Coil Resistance should be 4.4kΩ ± 20% at 20°C (68°F), measured with a pocket tester.

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The 1986 Yamaha YZ125S manual is a must-have for any owner. The download process was seamless, and I received my link quickly. The detailed sections on engine and chassis maintenance are particularly helpful. Highly recommend!