1991 Yamaha YZ125B Owner's Service Manual

1991 Yamaha YZ125B Service Documentation

• Official Yamaha OEM publication (P/N LIT-11626-07-55, 1st edition, June 1990) detailing the YZ125(B)/LC competition variant (3XJ-series).
• Delivered as an instant PDF download directly to your device the moment payment clears.
• Features a fully index-integrated structure spanning 175 pages, making system-level lookups fast and efficient on the workbench.
• Includes 8 exploded-view assembly diagrams and 35 detailed torque specification tables.

Manual Content and Coverage

Whether you are rebuilding the top end between motos or doing a complete off-season tear-down, this first edition manual serves as the foundational reference for the 1991 build. It provides the essential factory-specified clearances and tuning settings needed for professional-level workshop maintenance. You get comprehensive teardown, inspection, and assembly data for the liquid-cooled two-stroke engine, transmission, YPVS governor, and chassis components.

The documentation dives deep into competition preparation. It outlines complete carburetor tuning, front and rear suspension adjustments, brake system bleeding, and transmission oil procedures. Detailed cable routing diagrams and torque-check points ensure every critical frame fastener is properly secured. Always verify your setup and ensure all safety procedures are followed before taking the bike back to the track, as improper assembly can lead to equipment failure or injury.

Specification and Technical Data Preview

Engine components are strictly documented with their absolute wear limits and factory tolerances. For instance, the cylinder bore size for the 124 cm³ powerplant is specified at 56.00–56.02 mm, requiring a piston clearance of exactly 0.04–0.05 mm.

Electrical and cooling systems are equally detailed. The magneto pickup coil resistance is listed at 4.5–5.5 ohms at 20°C, and the total coolant capacity is rated at 0.9 liters. To save you time during reassembly, torque values for major components are clearly cataloged, such as the cylinder head nut torque spec of 30 Nm.