Yamaha YZ250X Owner's Service Manual, 2008 (P/N LIT-11626-21-44)

This is Yamaha's factory-issued Owner's Service Manual, P/N LIT-11626-21-44, first edition, June 2007 (cover code 1P8-28199-13), for the 2008 YZ250 closed-course competition motorcycle. The cover uses YZ250X; the specifications list YZ250W for the USA, Canada, Australia and New Zealand, and YZ250 for Europe and South Africa. Check the frame model label before ordering parts.

PDF Search, Bookmarks and Page Count

Search and diagram detail: The main chapters have searchable PDF text, while the warranty text and lettering within the overall wiring diagram are not searchable. Embedded bookmarks cover all seven chapters and numerous subsections. Small wiring labels are clearly readable when enlarged.

One printable, English-language PDF is supplied in a ZIP download, with 244 pages in total. This includes 14 pages of front matter containing the front cover, publication details, warranty and contents, two otherwise blank chapter pages, one closing blank page and the back cover.

Two-Stroke Engine, Chassis and Ignition Service

These are selected service topics, rather than a complete contents list. Additional sections explain the controls, cleaning and storage.

• Top-end repair: Exhaust pipe and silencer service, plus cylinder-head, cylinder, piston, ring, piston-pin, small-end-bearing and YPVS power-valve removal, inspection and reassembly.

• Lower engine and drivetrain: Clutch, kick and shift shafts, YPVS governor, CDI magneto, engine removal, crankcase separation, crankshaft, bearings and transmission service.

• Fuel and cooling: PWK38S carburetor and reed-valve service, radiator removal and water-pump disassembly, with inspection criteria and reassembly instructions.

• Brakes and chassis: Wheel and hub repair, steering-head work, swingarm and linkage inspection, master-cylinder and caliper service, fluid replacement and hydraulic bleeding.

• Suspension: Front-fork and damper disassembly, oil filling and air bleeding; rear-shock removal, spring replacement, bearing service, preload and damping adjustment.

• Electrical fault isolation: 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 and tuning: Maintenance intervals, pre-operation checks, break-in guidance, regional carburetor settings, jetting and throttle-opening charts, gearing, suspension setup, torque tables and wear specifications.

The repair depth makes this manual suited to experienced competition-bike owners and technicians with the specified special tools and measuring equipment. Yamaha recommends dealer maintenance for the front fork.

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. Step-by-step procedures for top-end, clutch and crankcase work support teardown planning and identifying parts that need replacement before reassembly.

Lower-end inspection covers crankshaft runout, main bearings, oil seals and case sealing. Transmission instructions address the main and drive axles, individual gears, shift cam, shift forks and guide bars, followed by operating checks.

Clutch repair covers the friction and clutch plates, springs, housing, boss, primary driven gear, push rods and push-lever shaft.

Yamaha requires the supplied set pin when releasing or installing the power-valve push rod; omitting it can damage YPVS parts.

Carburetor and Cooling-System Checks

The carburetor section covers float-height and needle-valve checks, jet and needle inspection, reed-petal inspection, and pilot-air and idle adjustment. Cooling-system work includes separate radiator-cap and system pressure tests, plus water-pump seal, shaft and impeller inspection.

Brake, Fork and Rear-Shock Coverage

Brake inspection extends to the discs, master-cylinder pistons and cups, caliper pistons and seals, and brake-hose installation. Front-fork repair includes the base valve, inner and outer tubes, bushings, oil and dust seals, and damper checks.

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.

Electrical Diagnosis and Trackside Tuning

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.

The throttle-position-sensor screw should not be loosened except during sensor replacement and calibration because an incorrect setting can reduce engine performance.

Trackside tuning relates the main, power and pilot circuits to throttle opening. Weather, altitude, surface conditions and operating symptoms guide carburetor selection, alongside secondary-gearing guidance and suspension-correction charts.

Workshop References and Precautions

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 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.

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.

A Preview of Piston-Fit and Ignition Test Specifications

The cylinder-and-piston section specifies a standard piston-to-cylinder clearance of 0.045–0.050 mm and a 0.1 mm service limit. Its matching chart pairs cylinder markings with the corresponding piston sizes and color markings.

For CDI magneto testing at 20°C (68°F), charging coil 1 is specified at 720–1,080 Ω and charging coil 2 at 44–66 Ω. The ignition chapter provides separate test-lead connections for these coils rather than treating them as one resistance range.