2008 Yamaha YZ250X / YZ250W / YZ250 Service Manual (P/N LIT-11626-21-44)

This is Yamaha's factory-issued Owner's Service Manual for the 2008 YZ250 two-stroke closed-course competition motorcycle. The cover identifies the publication as YZ250X, while the General Specifications chart lists YZ250W for the USA, Canada, Australia, and New Zealand and YZ250 for Europe and South Africa. Model-code coverage is 1P8D for the USA and Canada, 1P8E for Europe, and 1P8G for Australia, New Zealand, and South Africa. Check the frame model label before ordering parts. The repair depth makes this manual suited to experienced competition-bike owners and technicians with the specified special tools and measuring equipment.

• Document identity: A 244-page PDF covering the 2008 1P8 models; Yamaha P/N LIT-11626-21-44, cover code 1P8-28199-13, first edition, June 2007.
• Top-end, fuel, and cooling repair: Covers the exhaust pipe and silencer, radiator, PWK38S carburetor, reed valve, cylinder head, cylinder, piston, rings, piston pin, small-end bearing, and YPVS power-valve parts, with removal, inspection, repair, and reassembly procedures.
• Lower engine and drivetrain work: Details clutch service, kick and shift shafts, YPVS governor, water pump, CDI magneto, engine removal, crankcase separation, crankshaft and bearing work, transmission gears, shift cam, shift forks, and post-assembly operating checks.
• Chassis, brakes, and suspension: Includes wheel and hub repair, front and rear master-cylinder and caliper service, brake bleeding, fork and damper disassembly, steering-head work, swingarm and linkage inspection, and rear-shock spring and bearing service.
• Electrical fault isolation: Provides the complete wiring diagram and decision charts for the ignition system, engine-stop switch, ignition coil, CDI magneto, solenoid valve, throttle-position sensor, and Europe-only neutral switch.
• Maintenance, tuning, and shop reference: Supplies maintenance intervals, pre-operation checks, break-in guidance, market-specific PWK38S baseline settings, jetting and throttle-opening charts, gearing guidance, suspension setup data, special-tool numbers, torque tables, capacities, clearances, wear limits, and electrical test specifications.

Engine Repair Depth

Removal and disassembly sections open with exploded assembly views and job-order charts, followed by inspection criteria, replacement decisions, lubrication points, assembly notes, and final adjustments. The lower-end sequence covers crankshaft runout, main bearings, oil seals, case sealing, and reassembly, then addresses the main and drive axles, individual gears, shift cam, shift forks, guide bars, and operating checks.

Cooling-system work includes radiator-cap and system pressure testing, radiator removal, and water-pump seal, shaft, and impeller inspection. The carburetor section covers disassembly, float-height and needle-valve checks, jet and needle inspection, reed-petal inspection, and pilot-air and idle adjustment. Clutch repair reaches the friction and clutch plates, springs, housing, boss, primary driven gear, push rods, and push-lever shaft.

Brake, Fork, and Rear-Shock Coverage

The brake chapters cover pad and disc inspection, master-cylinder and caliper disassembly, piston, cup, and seal checks, brake-hose installation, fluid replacement, and hydraulic bleeding. Front-fork repair includes the damper assembly, base valve, inner and outer tubes, bushings, oil and dust seals, fork-oil filling, air bleeding, and final installation.

Rear-shock coverage is limited to removal, spring replacement, upper and lower bearing service, external inspection, installation, preload, and damping setup. It does not provide an internal damper-cylinder or nitrogen-reservoir overhaul. Yamaha warns against opening the pressurized cylinder or tank and restricts nitrogen-release disposal work to a Yamaha dealer.

Diagnostics, Tuning, and Visual References

Ignition troubleshooting follows a decision path through spark, harness connections, the stop switch, ignition coil, plug cap, CDI magneto, regional neutral switch, and CDI unit. Separate charts cover solenoid-valve operation and throttle-position-sensor coil testing, replacement, output adjustment, and input-voltage checks. Trackside tuning relates the main, power, and pilot circuits to throttle opening, with weather-, altitude-, surface-, and symptom-based carburetor guidance plus secondary gearing and suspension-correction charts.

Named visual references include the Cable Routing Diagram, Cylinder Head, Cylinder and Piston exploded assembly, Crankcase and Crankshaft job chart, Front Fork exploded views, Electrical Components and Wiring Diagram, and Effect of Setting Parts in Relation to Throttle Valve Opening chart. The special-tool list gives both North American and 90890-series identifiers, including the YU-1135-A/90890-01135 crankcase separator, YM-1189/90890-01189 flywheel puller, YM-A0948/90890-01502 fork-seal driver, and YM-91042/90890-04086 clutch holder.

Yamaha requires the supplied set pin when releasing or installing the power-valve push rod; omitting it can damage YPVS parts. The throttle-position-sensor screw should not be loosened except during sensor replacement and calibration because an incorrect setting can reduce engine performance.

Support the motorcycle securely on a suitable stand and use appropriate eye and hand protection before disassembly. Keep fuel away from ignition sources, prevent brake-fluid contamination, and do not open the nitrogen-charged rear-shock cylinder or reservoir.