1988–1990 Yamaha Enduro 50 / DT 50 / DT50U Service Manual (P/N LIT-11616-06–29)

• Exact factory coverage: Genuine Yamaha DT50U service manual for model code 3BK1, starting VIN *JYA3BKA0JC000101, and starting engine number 3BK-000101. The file is a 262-page PDF of Yamaha publication number LIT-11616-06-29**, 1st edition, December 1987.
• Documents engine removal, full disassembly, inspection, repair, reassembly, and adjustment of the cylinder and piston, crankshaft, crankcase, CDI magneto, clutch and primary drive, kick-start mechanism, shift shaft, shifter, and transmission.
• Covers Yamaha Autolube cable setting, pump-stroke adjustment, output inspection, and air bleeding, together with carburetor and reed-valve removal, cleaning, inspection, assembly, fuel-level setup, and idle adjustment.
• Walks through water-pump, thermostat, radiator, and cooling-system repair, including radiator-cap testing, system pressure and leak checks, coolant service, hose routing, and the coolant-flow chart.
• Provides chassis teardown and service for both wheels and drum brakes, front fork and seals, steering head, rear-shock removal and inspection, swingarm clearance and shim selection, and the drive chain and sprockets.
• Supplies the full DT50U wiring diagram plus circuit diagrams and test charts for ignition and starting, charging, lighting, signals, oil-level warning, sidestand and neutral interlock, temperature gauge, and cooling-system electrical faults.

Exact DT50U Build Identification

The specification section identifies a liquid-cooled, forward-inclined single-cylinder 49.3 cc two-stroke with reed-valve induction, Yamaha Autolube, a wet multi-disc clutch, and a constant-mesh six-speed transmission. The model code and starting VIN and engine number provide a much better fitment check than relying on a generic “DT50” name.

Factory reference data covers engine, chassis, and electrical specifications; component-specific torque tables; wear and service limits; clearances and runout limits; fluid capacities; lubrication points; cable routing; and periodic maintenance. Engine repair tools are identified by part number, including the YM-01312-A fuel-level gauge, YM-91042 clutch holder, YU-01235 rotor holder, YM-01189 rotor puller, YU-01135 crankcase separating tool, and YU-90050/YU-90063 crankshaft installer and adapter. Chassis tools include the YU-33975 steering ring-nut wrench and the YM-01326/YM-01300-1 front-fork holding tools.

Engine, Fuel, Cooling, and Chassis Repair Scope

Routine service coverage reaches well beyond an oil-change checklist. The manual addresses idle speed, throttle and clutch free play, spark-plug inspection, ignition timing checks, transmission-oil service, air-filter cleaning, brake adjustment, chain and steering adjustment, spoke tightening, battery and fuse inspection, and headlight aiming. Autolube bleeding is tied to the situations that actually require it: initial setup, an oil tank that has run dry, or any disconnected oil-system line. Pump-stroke adjustment and output inspection are covered separately.

The engine-overhaul chapter distinguishes major parts that can be serviced with the engine still in the frame from crankcase, crankshaft, and transmission work that requires deeper teardown. It then covers crankcase separation, crankshaft installation, transmission and shift-fork setup, clutch-stack and primary-drive assembly, CDI magneto service, piston and ring installation, engine remounting, and final clutch, chain, cooling, and Autolube checks.

Cooling and fuel-system repair sections deal with the water-pump impeller, shaft, gear, and oil seal; thermostat and radiator removal; radiator-cap and system pressure testing; carburetor and reed-valve overhaul; float-height and fuel-level checks; and final idle and cable adjustment. Chassis procedures include wheel-bearing and drum-brake service, static wheel balancing, fork damper and seal work, steering-bearing service, swingarm side-clearance calculation and shimming, and drive-chain master-link installation. The rear shock is treated as a sealed, nitrogen-charged assembly: the manual covers handling, removal, inspection, installation, and disposal precautions, not an internal shock rebuild.

Several cautions are specific to this motorcycle. The piston pin is not to be driven out with a hammer, and the crankcase halves must not be forced apart or struck on their gasket surfaces, avoiding damage to the piston-pin area and crankcase mating faces. The manual also warns against spinning cleaned bearings with compressed air because it damages the bearing surfaces. Orientation-sensitive items include the numbered shift forks, piston and ring locating points, conical clutch washers, thermostat air-bleed hole, and drive-chain master-link clip.

Electrical Diagnosis, Diagrams, and Troubleshooting

The electrical chapter uses circuit-by-circuit tests rather than relying only on a color schematic. It covers no-spark diagnosis; spark-plug-cap, ignition-coil, source-coil, and pickup-coil checks; sidestand and neutral interlock tests; charging output and coil checks; lighting output and dimmer-switch tests; flasher, brake-light, neutral-light, oil-warning, and horn diagnosis; and temperature-gauge and thermo-unit testing. One ignition-control logic page is explicitly labeled “For Europe,” while the ignition troubleshooting includes an “Except for Singapore” note, making the regional electrical scope visible before those circuits are applied.

Useful visual references include the coolant-flow chart, cable-routing drawings, clutch/primary-drive and shifter/transmission exploded views, front-fork and swingarm exploded views, system-specific electrical circuit diagrams, and the final full DT50U wiring diagram. The symptom charts cover hard starting, poor idle and high-speed performance, faulty shifting, clutch slipping or dragging, kick-start problems, weak brakes, fork oil leakage or malfunction, unstable handling, signal and lighting faults, and overheating or overcooling.

This factory publication was written for Yamaha dealers and qualified mechanics and assumes basic motorcycle repair knowledge. Cooling-system work involves hot, pressurized coolant; follow the manual’s safety warnings and support procedures before disassembly.