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 uses the designation YZ250X, while the specification chart identifies the market models as YZ250W for the USA, Canada, Australia, and New Zealand, and YZ250 for Europe and South Africa. Confirm the applicable 1P8 model code before ordering; coverage is limited to this 2008 publication.

• Coverage and document identity: A 244-page PDF for YZ250X/YZ250W/YZ250 model codes 1P8D, 1P8E, and 1P8G; Yamaha P/N LIT-11626-21-44, cover code 1P8-28199-13, first edition, June 2007.
• Top-end and induction repair: Covers the exhaust system, radiator, PWK38S carburetor, reed valve, cylinder head, cylinder, piston, rings, piston pin, and YPVS power-valve components, 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 service, transmission gears, shift cam, and shift forks.
• Chassis, brakes, and suspension: Includes wheel and hub service, front and rear brake master-cylinder and caliper repair, hydraulic bleeding, front-fork disassembly and damper service, steering-head work, swingarm and linkage inspection, and rear-shock spring and bearing service.
• Electrical diagnosis: Provides the complete wiring diagram plus fault-isolation charts and test procedures for the ignition system, engine-stop switch, ignition coil, CDI magneto, solenoid valve, throttle-position sensor, and the Europe-only neutral switch.
• Tuning and shop reference: Supplies market-specific PWK38S baseline settings, jetting and throttle-opening charts, sprocket-ratio guidance, front- and rear-suspension setup data, special-tool numbers, torque tables, capacities, clearances, wear limits, and cable-routing views.

Engine and Chassis Repair Depth

Yamaha organizes removal and disassembly sections around exploded assembly views and job-order charts, then follows them with inspection criteria, replacement decisions, assembly notes, lubrication points, and final adjustments. The engine chapters support both a routine top-end repair and a full lower-end teardown. The cylinder section addresses the head, bore, piston, rings, pin, small-end bearing, and power-valve hardware; the crankcase section covers case separation, crankshaft runout, main bearings, oil seals, and reassembly. Transmission coverage extends through the main and drive axles, individual gears, shift cam, shift forks, guide bars, and operational checks after assembly.

Fuel and cooling procedures cover radiator-cap and cooling-system testing, radiator removal, water-pump inspection, carburetor disassembly, float and jet checks, reed-valve inspection, pilot-air and idle adjustment, and regional carburetor specifications. Clutch repair includes the plates, springs, housing, boss, push mechanism, and related wear checks.

Brake coverage includes pad service, disc inspection, master-cylinder and caliper disassembly, piston and seal inspection, hose installation, fluid replacement, and system bleeding. The front-fork chapter addresses the damper assembly, base valve, inner and outer tubes, bushings, oil and dust seals, fork-oil filling, air bleeding, and final installation. Steering bearings, wheel bearings, spokes, drive chain, swingarm, relay arm, connecting rod, and linkage bearings are handled in separate repair sections.

The rear-shock chapter has a clear scope limit. It covers removal, spring replacement, upper and lower bearing service, external inspection, installation, preload, and damping setup, but not an internal damper-cylinder or nitrogen-reservoir overhaul. Yamaha warns against opening those pressurized parts and directs disposal work to a dealer.

Electrical Diagnosis, Tuning, and Shop Reference

Electrical troubleshooting is laid out as decision charts rather than a loose list of resistance values. The ignition chart moves 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 testing, replacement, output adjustment, and input-voltage checks.

The tuning chapter is built around track-side setup. It relates main, power, and pilot circuits to throttle opening; provides weather-, altitude-, road-condition-, and symptom-based carburetor guidance; and covers needle position, jet-needle selection, pilot-air adjustment, and spark-plug heat range. Chassis tuning addresses secondary gearing, tire pressure, fork oil and spring selection, rear-spring setup, and symptom-based front and rear 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. Tool references identify the crankcase separator and installer, flywheel puller and rotor holder, fork cap and seal tools, and clutch holder. Cooling and electrical work lists the radiator tester, ignition checker, pocket tester, and digital tachometer, with North American and 90890-series part numbers where applicable.

Several repair traps are called out directly. The supplied set pin must be used when releasing or installing the power-valve push rod, or YPVS parts can be damaged. The crankshaft and case halves are handled with the specified separating and installing tools; hammering the crankshaft or forcing uneven case separation risks damage to the bearings and mating surfaces. The throttle-position-sensor screw is not a casual adjustment point—loosening it outside the replacement and calibration procedure can reduce engine performance.

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