1975–1980 Yamaha RD125 / RD125B / RD125DX Owner's Manual (P/N 507-28199-81)

• Official 86-page Yamaha Motor Co., Ltd. publication (P/N 507-28199-81), printed in Japan in February 1975.
• Covers the 1975–1980 Yamaha RD125, RD125B, and RD125DX models, including the specific hydraulic braking system variants found on the DX.
• Documents initial technical specifications and service intervals for the entire series build.
• Features 6 detailed flow charts dedicated to fuel, compression, and ignition system troubleshooting.
• Explains step-by-step procedures for clutch adjustment, carburetor tuning, ignition timing, drive chain tensioning, and headlight beam alignment.
• Outlines component-specific servicing for the steering damper, fuel petcock, air filter element, throttle cable, and battery fluid.

Manual Content Overview

This PDF manual is the primary reference for anyone maintaining these classic two-stroke machines. Instead of generic overviews, it breaks down the exact requirements needed to keep the bike running smoothly. The documentation organizes vehicle information into four distinct sections: exterior identification, control functions, riding fundamentals, and periodic maintenance schedules. It details the routine diagnostic inspections your Autolube oil tank, transmission, fuel delivery, and electrical circuits require. It also covers the minor repair tasks and adjustments you will inevitably perform in the workshop. By providing step-by-step instructions for high-labor procedures like tuning the carburetor idle speed, adjusting the clutch push-screw, and accurately calibrating the ignition timing, this guide helps you avoid expensive professional rates at a vintage specialty shop. Because working on vintage motorcycle systems carries inherent physical risks, always verify torque specifications and wear appropriate protective equipment before handling mechanical components.

Specification and Technical Data Highlights

The technical tables are where this documentation really delivers for bench work, providing immediate workshop utility by outlining the exact factory tolerances that prevent costly trial-and-error damage to soft vintage aluminum components. You will find precise lubrication charts calling out the correct motor oil and grease for components like brake camshafts, wheel bearings, and drive chains. To further support your workflow, the text utilizes specific visual aids such as a periodic inspection chart, shift pedal pattern views, drive chain alignment drawings, and headlight beam adjustment schematics.

Cylinder head spark plug tightening torque is strictly set at 2.5–3.0 m-kgs, and transmission oil capacity is defined at exactly 750 ± 50 cc. Ignition timing is critical on these two-strokes; accordingly, the contact breaker point gap is specified at 0.3–0.4 mm. You will also find dedicated hydraulic routing and reservoir data for the RD125DX front brake.

When servicing these classic Yamaha twins, mechanics often encounter severe tuning issues stemming from neglected Autolube pumps or hardened crankshaft seals, which can quickly lead to lean-running conditions and catastrophic piston seizures. Additionally, relying purely on visual alignment for the contact breaker points is a notorious pitfall; utilizing a dial indicator to set exact factory ignition timing is imperative to prevent destructive pre-ignition on these air-cooled motors.