1991 Yamaha YZ250B Owner's Service Manual (P/N LIT-11626-07-56)

• Factory document and exact application: Covers the 1991 Yamaha YZ250B closed-course competition model as 3XK1 for Europe, 3XK2 for the USA, Canada, and other markets, and 3XK4 for Australia and New Zealand. Yamaha P/N LIT-11626-07-56, 1st Edition dated June 1990, supplied as a 262-page PDF.
• Fuel-system and top-end repair: Details TM38SS Mikuni carburetor and reed-valve removal, inspection, setup, and installation, along with cylinder-head, cylinder, piston, ring, small-end bearing, and YPVS power-valve service.
• Bottom-end and drivetrain work: Covers the wet multi-disc clutch, primary gears, kick and shift mechanisms, YPVS governor, CDI magneto removal, engine removal and installation, crankcase splitting, crankshaft service, five-speed transmission, shift cam and forks, radiator, and water pump.
• Wheels and hydraulic brakes: Provides wheel-bearing replacement and wheel inspection, plus front and rear caliper, piston-seal, master-cylinder, brake-disc, hose, fluid-filling, and air-bleeding procedures.
• Steering and suspension service: Includes steering bearings, swingarm and relay-arm inspection, complete upside-down front-fork disassembly and assembly, seal replacement, oil-level setup, damping adjustment, and rear-shock removal, spring service, and external inspection.
• Ignition diagnosis and race tuning: Supplies the CDI wiring diagram and a fault-isolation sequence for the spark plug, connections, stop button, ignition coil, pickup and charging coils, and CDI unit, followed by carburetor, gearing, suspension, handlebar-position, and track-setting guidance.
• Factory reference data: Includes component-specific torque tables, capacities, approved fluids and lubricants, wear limits, clearances, electrical test values, cable routing, regional setting-part tables, exploded assembly drawings, and Yamaha special-tool numbers.

Built Around the 3XK Regional Variants

The identification section lists the actual starting numbers used by each market. Europe begins at frame and engine number 3XK-000101. USA and Canadian machines use VIN JYA3XKW0MA008101 and engine number 3XK-008101; Australian machines use VIN JYA3XKT0MA019101 and engine number 3XK-019101. New Zealand frame and engine numbers begin at 3XK-019101, while the other-market frame and engine sequence begins at 3XK-008101.

Those market divisions matter beyond the identification page. The specification and setting sections distinguish European gearing, carburetor calibration, fork springs and oil setup, and rear-shock spring and damping data from the other versions. Separate fuel and spark-plug notes also apply to Australia, Canada, and South Africa. This allows parts and setup data to be matched to the correct 3XK build before repair work begins.

Mechanic-Oriented Procedure Format

Yamaha calls this an Owner's Service Manual, but the procedure format is explicitly organized for a mechanic. Each major repair section combines an illustrated removal order, job chart, removal notes, inspection criteria, and assembly or installation information. Although the opening chapters cover controls, premix fuel and oil, pre-operation checks, starting, break-in, torque checks, cleaning, and storage, the internal-engine, hydraulic-brake, and fork procedures are best suited to an experienced two-stroke mechanic or technically capable owner with the specified measuring equipment and service tools.

The rear shock section has an important boundary: it covers removal, spring handling, external inspection, adjustment, and dealer-only disposal guidance, but not internal damper disassembly or nitrogen recharging. Likewise, the electrical chapter is an ignition-system repair section for the CDI magneto, CDI unit, coil, stop button, leads, and spark plug; it does not cover battery or lighting systems.

Tools, Drawings, and Repair Cautions

The special-tool index cross-references the YM/YU numbers used in the USA and Canada with 90890-series numbers for other markets. Notable examples include the crankcase separator YU-01135/90890-01135, fork-seal driver YM-38853/90890-01442, damper-rod holder YM-1423/90890-01423, Yamaha Pocket Tester YU-03112/90890-03112, and Ignition Checker YM-34487/90890-06754.

Named visual references include the Cable Routing Diagram and Electrical Components and Wiring Diagram, supported by exploded and sectional views for the cylinder and piston, crankcase and crankshaft, front fork, and front and rear brake assemblies. The suspension chapter adds symptom-and-remedy charts plus a setting-record table for track testing.

The fork section warns not to bottom the inner tube during separation because the oil-lock piece can be damaged; it also explains that the damper rod can damage its internal valve if allowed to fall into a vertically held tube during assembly. The crankcase section warns against forcing the case halves apart or striking their gasket surfaces, which can damage the case and sealing faces. Support the motorcycle securely, release fork air pressure before cap removal, and keep gasoline away from heat, sparks, and open flame.