1990–2000 Yamaha RT100A Service Manual (P/N LIT-11616-07-35)

• Factory coverage: A 170-page PDF of Yamaha Service Manual P/N LIT-11616-07-35, first edition January 1990, for the RT100A model code 3UL1. Machine identification starts at VIN JYA3ULW0*LC000101 and engine serial 3UL-000101.
• Engine repair depth: Covers engine removal and remounting plus disassembly, inspection, repair, and assembly of the top end, crankshaft and crankcase, wet multi-disc clutch, primary drive, kick-start mechanism, shift system, and constant-mesh five-speed transmission.
• Fuel and oiling systems: Details the Mikuni VM22SS carburetor, I.D. 3UL00, reed valve, and Yamaha Autolube system, including carburetor teardown and setup, pump adjustment, output inspection, and air bleeding.
• Chassis procedures: Documents wheel and drum-brake repair, front-fork disassembly and seal service, steering-head and handlebar work, rear shock absorber and swingarm inspection, and drive-chain and sprocket service.
• Electrical diagnosis: Provides CDI magneto ignition schematics, the RT100A wiring diagram, coil and spark testing, ignition-timing checks, and system-specific fault isolation.
• Diagrams and factory data: Contains 15 full-page exploded assembly views, cable-routing drawings, lubrication charts, maintenance tables, component torque tables, capacities, inspection limits, clearances, carburetor data, and electrical test specifications.

What the Manual Documents

The publication is built around the 3UL1 configuration: a 97 cc air-cooled two-stroke single with reed-valve induction, separate Yamaha Autolube lubrication, a Mikuni VM22SS carburetor, wet multi-disc clutch, chain final drive, and five-speed gearbox. Its starting VIN and engine-number data give a shop or owner a firm identification point before choosing repair procedures or ordering internal parts.

Yamaha separates in-frame service from work that requires a complete teardown. The cylinder head, cylinder, piston, clutch and primary drive, kick axle, shift shaft, and CDI magneto can be serviced with the engine mounted after the surrounding parts are removed. Crankshaft, transmission, and internal shifter repair continues through engine removal, crankcase separation, component inspection, reassembly, adjustment, and final remounting.

Inspection coverage extends to piston and ring condition, piston-pin and bearing wear, clutch plates and springs, primary gears, kick-start parts, shift forks, transmission shafts and gears, crankshaft alignment, crankcase condition, and Autolube pump output. The related tables provide the factory wear limits, clearances, tightening data, lubrication points, and assembly specifications for those jobs.

The carburetion chapter follows the VM22SS through removal, disassembly, cleaning, inspection, assembly, installation, fuel-level checking, and final adjustment. Reed-valve service is handled separately. Routine shop procedures cover idle and throttle settings, Autolube adjustment and bleeding, ignition timing, transmission oil, clutch free play, air-filter service, fuel and exhaust checks, brakes, chain, steering head, wheels and spokes, fork inspection, and rear-shock adjustment.

Chassis chapters take both wheel assemblies through removal, bearing and brake inspection, installation, and final checks. Separate sections handle the telescopic fork, steering-head bearings and handlebar, rear shock absorber and swingarm, and chain and sprockets. Electrical coverage is limited to the CDI magneto ignition and engine-stop circuit; this is not a lighting, charging, battery, or electric-start service manual.

Factory troubleshooting charts isolate hard starting, poor idle or higher-speed performance, hard shifting and gear jump-out, clutch slip or drag, kick-start faults, weak braking, fork oil leakage, unstable handling, and overheating. The ignition chapter adds a circuit diagram and test sequence for the spark plug, engine-stop switch, CDI unit, source and pickup coils, ignition coil, and related wiring.

Factory Diagrams, Tools, and Reference Data

The 15 exploded views are full-page assembly references. Representative sheets cover the crankshaft, transmission, clutch and primary drive gear, carburetor, front fork, and steering head and handlebar. Cable-routing views identify the control cables, CDI lead, engine breather, oil hose, and oil-delivery hose.

The special-tool section identifies equipment for the major repair jobs, including the YM-01189 flywheel puller, YU-01135 crankshaft separating tool, YU-90050 crankshaft installing tool with YM-90063 adapter, YM-33963 fork-seal-driver weight with YM-33281 adapter, and YM-34487 dynamic spark tester. Tune-up references also list the timing light, fuel-level gauge, tachometer, and pocket tester by Yamaha tool number.

The manual calls out repair traps that can ruin usable parts. Forcing the crankcase halves apart or striking the gasket mating surface can damage the aluminum case and its sealing faces; during top-end assembly, a piston-ring end that is not seated at its locating pin can be caught and damaged as the cylinder is fitted.

This factory service manual assumes a working knowledge of motorcycle repair. Because it covers fuel-system work, ignition testing, brake service, and wheel or fork removal, the motorcycle should be securely supported and the publication’s warnings, specified tools, and inspection criteria followed throughout the job.