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

Yamaha’s IT490(L)/IT250(L) Owner’s Service Manual, P/N 29V-28199-70, combines operating guidance with maintenance, troubleshooting, and repair procedures. This bilingual English/French edition was first published in July 1983 and covers the 1984 models.

PDF Reading, Wiring Detail, and Page Layout

Search, bookmarks, and diagrams: PDF text search and embedded bookmarks are not available. The separate wiring diagrams have small component labels and wire-color codes that require zooming; rotating the diagrams also makes them easier to read.

The ZIP contains one printable 96-page PDF, comprising 94 two-page spreads plus the front and back covers. Both covers are included in the total.

Two-Stroke Engine, Monocross, and Electrical Service

The following selected coverage highlights outline the main workshop sections. Other topics include starting and break-in guidance, fuel-cock strainer cleaning, and storage preparation.

• Engine and intake: Step-by-step top-end removal, inspection, and assembly, together with carburetor, Yamaha Energy Induction System (Y.E.I.S.), reed-valve, and exhaust service.

• Clutch and transmission: Clutch inspection and adjustment, kickstarter and shifter repair, crankcase separation, transmission installation, and crankshaft inspection and fitting.

• Wheels and brakes: Wheel removal and installation, rim and spoke checks, drum-brake inspection, two-leading-shoe adjustment, and drive-chain and sprocket service.

• Suspension and steering: Front-fork disassembly, seal and bushing replacement, steering-head bearing service, and Monocross shock, relay-linkage, and swingarm procedures.

• Electrical diagnosis: Fault-finding charts for ignition, lighting, and charging, supported by electrical-component locations and separate IT490 and IT250 wiring diagrams.

• Workshop references: Maintenance schedules, lubrication points, torque tables, capacities, wear limits, adjustment specifications, electrical test data, cable-routing drawings, and numbered special tools.

The repair sections suit experienced owners and mechanics familiar with precision measurement, electrical testing, and specialist engine and suspension tools; the operating section also explains controls and basic checks.

Model Identification and Electrical Equipment

The model codes distinguish the IT490(L) 29W and 45K versions from the IT250(L) 29V and 45J versions. Yamaha specifically identifies the 45K and 45J versions as having no turn signals, brake light, main switch, or battery.

That equipment distinction helps match the electrical checks and replacement components to the machine. The carburetor specifications also distinguish the IT490’s Mikuni VM38SS from the IT250’s VM36SS.

Intake, Top-End, and Internal Engine Repair

Carburetor and induction: The fuel-system material covers passages, floats, inlet-valve and seat condition, main-jet replacement, and float-height measurement. Y.E.I.S. coverage addresses the air chamber, hose, and connections, while the reed-valve section examines petal condition, sealing, and installation orientation.

Cylinder and piston inspection: Exhaust decarbonizing and cylinder-head inspection lead into bore measurement, taper and out-of-round checks, piston measuring points, oversize options, ring clearances, and piston-pin and bearing inspection.

The piston-pin caution explains that hammering a sticking pin can damage the connecting rod, piston, and bearing. Crankcase-separation notes address uneven loading and damage to gasket surfaces when a case half is forced apart.

Clutch and lower end: Beyond plate and spring inspection, the manual explains pressure-plate alignment, release-mechanism adjustment, and identification marks for matched primary gears. Internal repair material includes shift-fork and cam inspection, bearing and oil-seal work, and crankshaft installation. Separate transmission assembly drawings distinguish the two models’ gear stacks, spacers, and component positions.

Drum Brakes, Forks, and Monocross Suspension

The chassis chapter details front-brake cam synchronization, brake-shoe condition, wheel runout, spoke tension, chain wear, and sprocket condition. Wheel-bearing inspection is covered; bearing replacement is referred to a Yamaha dealer.

Fork instructions extend through oil replacement, air release, disassembly, tube and bushing inspection, seal installation, and reassembly. Steering-bearing races, linkage lubrication, and swingarm washers and shims receive specific attention. Swingarm-bearing replacement is also referred to a dealer.

The front-fork exploded view and Monocross “De Carbon” shock layout identify the service components. Rear-shock coverage includes external settings, spring removal and installation, and complete-unit removal and refitting. Internal shock-body or reservoir disassembly is expressly prohibited, and the disposal procedure is reserved for Yamaha dealers.

Electrical Fault Isolation and Workshop Equipment

The ignition charts distinguish spark-plug and stop-switch faults from ignition-coil, connector, pickup-coil, source-coil, and CDI-unit problems. Lighting and charging sections add output checks, regulator and rectifier tests, battery and fuse checks, and harness-continuity testing.

The symptom-based appendix connects starting difficulty, poor high-speed performance, overheating, shifting problems, clutch faults, and chassis symptoms with possible causes. Together with the test charts, it supports diagnosis before components are selected for replacement.

Illustrations include transmission assembly views, the fork exploded view, the Monocross layout, ignition fault charts, model-specific wiring diagrams, and cable-routing drawings.

The tool references identify the Yamaha Pocket Tester 90890-03112, crankcase separator 90890-01135, and crankshaft installer 90890-01274. Fork work references holder and adapter 90890-01327/90890-01326 and seal/bushing tools 90890-01367/90890-01374.

Detailed carburetor and suspension tuning is assigned to a separate Race Preparation and Tuning Manual, which is not included. 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.

A Preview of Piston and Clutch Inspection Dimensions

Normal piston-to-cylinder clearance is specified as 0.070–0.075 mm for the IT490(L) and 0.045–0.050 mm for the IT250(L). The accompanying measuring-point illustrations explain how piston diameter relates to the clearance assessment.

For both models, clutch friction plates have a standard thickness of 3.0 mm and a wear limit of 2.7 mm. The clutch section pairs these dimensions with plate-condition and measurement checks.