Yamaha IT490 IT250 1984 Owner's Service Manual (P/N 29V-28199-70)

• Yamaha cover code 29V-28199-70, first edition dated July 1983; supplied as a 96-page bilingual English/French PDF for the IT490(L) and IT250(L).
• Model and serial identification covers IT490(L) codes 29W and 45K from frame/engine numbers 29W-003101 and 45K-000101, plus IT250(L) codes 29V and 45J from 29V-003101 and 45J-000101.
• Engine repair coverage runs from carburetor and Y.E.I.S. inspection through reed valves, exhaust, cylinder head, cylinder, piston assembly, clutch, kickstarter, shifter, crankcase, transmission, and crankshaft work.
• Chassis procedures address wheel removal and installation, drum brakes, chain and sprockets, fork oil and seal service, steering-head bearings, the Monocross “De Carbon” rear shock, relay linkage, and swingarm.
• Electrical fault charts test the ignition, lighting, and charging systems, supported by electrical-parts locations and separate IT490 and IT250 wiring diagrams.
• Factory reference data provides maintenance schedules, torque tables, capacities, wear and clearance limits, adjustment data, electrical test values, cable-routing views, and a numbered special-tool list.

Exact Model Coverage

This Yamaha Owner’s Service Manual combines operating information with detailed maintenance and repair material for the IT490(L) and IT250(L). It is suited to experienced owners and mechanics who are comfortable using measuring instruments, electrical test equipment, and engine or suspension service tools; it does not teach basic workshop practice.

The appendix separates the two machines clearly. The IT490 uses a 487 cc air-cooled two-stroke single, a five-speed constant-mesh transmission, and a Mikuni VM38SS carburetor. The IT250 uses a 246 cc engine, a six-speed transmission, and a Mikuni VM36SS. Yamaha also distinguishes the 45K and 45J versions: those variants do not have turn signals, a brake light, a main switch, or a battery. That distinction matters when selecting the applicable wiring diagram, charging checks, and replacement parts.

Engine and Drivetrain Repair

The engine chapter goes well beyond tune-up data. It covers carburetor inspection, main-jet replacement, and float-level checking; Y.E.I.S. air-chamber and hose inspection; reed-petal condition and sealing; muffler removal and carbon cleaning; and top-end removal, measurement, inspection, and assembly. Piston-diameter measuring points, cylinder taper and out-of-round limits, available oversizes, ring clearances, and model-specific piston clearances are tabulated rather than treated generically.

For deeper repair work, the manual documents clutch removal, plate and spring inspection, pressure-plate alignment, mechanism adjustment, and matched primary-gear identification. Kickstarter and shifter sections lead into engine removal, crankcase separation, transmission inspection and installation, bearing and oil-seal service, crankshaft checks, and crankshaft installation. The transmission drawings show the IT490 five-speed and IT250 six-speed gear stacks, shift forks, cam, spacers, and installation order.

Two factory cautions illustrate the level of detail. Hammering a sticking piston pin can damage the connecting rod, piston, and bearing. During crankcase separation, the tool must remain square and the case halves must come apart evenly; forcing a hung half or striking a gasket surface risks case damage.

Chassis, Suspension, and Electrical Content

The chassis section covers wheel bearings, spoke and rim checks, brake-shoe inspection, two-leading-shoe front brake synchronization, chain wear and alignment, and sprocket replacement. Fork coverage includes oil replacement, air release, removal, disassembly, seal and bushing replacement, inspection, and reassembly. Steering-head bearing work and Monocross linkage/swingarm removal, inspection, lubrication, and installation are also shown.

Useful illustrations include the five- and six-speed transmission assembly views, front-fork exploded section, Monocross rear-shock layout, ignition fault-isolation charts, separate model wiring diagrams, and the final cable-routing drawings. The electrical charts narrow no-spark faults through the plug, stop switch, ignition coil, connectors, CDI pickup/source coils, and CDI unit. Lighting and charging checks cover output, regulator, rectifier, battery, fuse, coils, and harness continuity.

Special Tools and Scope Limits

The special-tool pages identify the Yamaha Pocket Tester 90890-03112, crankcase separating tool 90890-01135, crankshaft installer 90890-01274, fork-cylinder holder and adapter 90890-01327 and 90890-01326, and fork seal/bushing tools 90890-01367 and 90890-01374, among others. The appendices add symptom-based troubleshooting for starting, high-speed performance, overheating, transmission, clutch, steering, wheels, brakes, and lights.

Detailed carburetor tuning and suspension tuning are assigned to a separate Race Preparation and Tuning Manual. The rear-shock section covers external settings, spring work, removal, and installation, but warns against disassembling the pressurized shock body or reservoir; shock disposal is marked for Yamaha dealers only. Fuel-system work, pressurized forks, and the nitrogen-charged rear shock present fire and stored-pressure hazards, so major repair work should be handled only with the specified equipment and appropriate experience.