Yamaha IT250H/IT465H 1978–1982 + IT250L/IT490L Owner’s Service Manual Set (P/N 5L4-28199-20)

Use the publication matching your machine’s model code; the volumes document different engine, chassis, and electrical configurations.

Detailed L-series carburetor and suspension tuning is referred to Yamaha’s separate Race Preparation and Tuning Manual, which is not included.

PDF Search, Bookmarks, and Wiring Detail

Navigation and diagram readability: Neither PDF supports text search. The H-series file has section bookmarks; the L-series file has none. H-series wiring diagrams have faint, broken lines and partly illegible labels, even when enlarged. Small L-series wiring labels require zooming. Two H-series wheel-service pages are out of printed order.

ZIP download containing two printable PDFs with 169 PDF pages total, including the original covers and front matter. The L-series file is mainly two-page spreads.

Two-Stroke Engine, Chassis, and Electrical Service

This selected content overview highlights the main service areas. Further topics include fuel-cock strainer cleaning and preparation for storage.

• Engine and transmission repair: Engine removal, step-by-step top-end work, piston/ring inspection, clutch, kickstarter and shifter service, crankcase separation, crankshaft installation, and internal gearbox repair.

• Intake and exhaust: Carburetor removal, disassembly, inspection and reassembly, jet/float adjustments, Yamaha Energy Induction System (Y.E.I.S.) checks, reed-valve service, and muffler maintenance.

• Chassis and suspension: Wheel and sprocket repair, brake inspection and adjustment, steering-head service, front-fork overhaul, Monocross De Carbon shock adjustment, and swingarm/linkage work.

• Electrical diagnosis: Four model-specific wiring diagrams, component-location and cable-routing views, CDI testing, lighting and charging diagnosis, battery checks, and symptom-based troubleshooting charts.

• Maintenance and reference data: Owner checks, lubrication schedules, air-filter service, break-in procedures, special-tool charts, component torque tables, wear limits, clearances, capacities, and electrical test specifications.

Owners can use the routine maintenance sections, while internal repairs suit readers experienced with precision measurement and the specified special tools.

Intake and Internal Engine Inspection

Carburetor sections distinguish jet replacement from float and valve-seat inspection and show tuning-part choices. Y.E.I.S. coverage includes chamber, hose, and connection checks; the H-series material identifies this system specifically with the IT250H.

Transmission inspection examines shift forks, cam grooves, shafts, gear teeth, and engagement dogs. Crankshaft coverage includes measurement and installation; the H-series instructions refer out-of-limit crankshaft repair to a Yamaha dealer.

Hammering a stuck piston pin can damage the connecting rod, piston, and bearing. The crankcase cautions also address damage from forcing unevenly separated cases or striking machined sealing surfaces.

Forks, Brakes, and Monocross Suspension

The L-series chassis section includes two-leading-shoe front-brake linkage adjustment and relay-arm/connecting-rod removal, lubrication, and reassembly. Fork procedures cover oil seals and bushings as well as inner-tube inspection.

The H-series suspension-tuning charts relate bottoming or harshness to air pressure, oil viscosity, spring choice, and damping adjustments. Both manuals prohibit opening the pressurized De Carbon shock cylinder or reservoir; their shock procedures cover removal, inspection, spring work, and external adjustment.

Support the motorcycle securely and follow the publications’ fuel, battery, spring, and pressurized-suspension warnings before engine, chassis, or electrical work.

CDI Fault Isolation and Electrical Variants

The ignition flowcharts help trace a weak or missing spark through plug, cap, stop-switch, and coil checks before CDI-unit replacement. Lighting and charging sections add regulator, rectifier, continuity, and output-current tests.

IT250(L) 45J and IT490(L) 45K omit the flashers, brake light, main switch, and battery. These differences matter when selecting the applicable electrical checks.

General troubleshooting charts separate hard starting, poor high-speed performance, overheating, shifting faults, clutch slip or drag, chassis problems, and lighting complaints.

Special Tools and Repair Drawings

H-series tool references include flywheel holder 90890-01235, puller 90890-01189, crankcase separator 90890-01135, crankshaft setting tools, steering-nut wrench 90890-01051, dial-gauge set 90890-01252, and timing light 90890-03109.

The L-series lists Yamaha pocket tester 90890-03112, crankshaft installing tools, a fork-cylinder holder and adapter, fork seal/bushing tools, and a drive-chain cutter.

Illustrations include carburetor/Y.E.I.S. layouts, cylinder-and-piston exploded views, clutch/transmission assemblies, crankcase separation/installation drawings, front-fork sections, and Monocross shock/linkage views. Model-specific reference tables keep carburetor, clutch, ignition, and suspension data separate where configurations differ.

Piston Clearance and Clutch Wear: Specification Preview

The H-series piston specifications list skirt clearance of 0.045–0.050 mm for IT250H and 0.070–0.075 mm for IT465H.

For both H models, the clutch data specifies new friction-plate thickness of 3.0 mm and a wear limit of 2.7 mm.