1977–1982 Yamaha GT80, GTMXE, GT80G, GT80J, DT80J, DT100D, DT100G, DT100J Factory Service & Supplementary Manual (P/N LIT-11616-03–05)

• 211-page PDF collection of Yamaha factory literature: one-page combined index; 31-page DT80J/DT100J supplement P/N LIT-11616-03-05; 22-page GT80G supplement P/N LIT-11616-01-68; 70-page GT80E/GTMXE manual P/N LIT-11616-00-75; 22-page DT100G supplement P/N LIT-11616-01-67; and 65-page DT100D manual P/N LIT-11616-00-36.
• 1977-1982 model-era identification: GT80E 2F4-000101, GTMXE 367-400101, GT80G 3J8-000101, DT80J frame 3J8-150101/engine 3J8-070101, DT100D 1T9-000101, DT100G 3A3-000101, and DT100J 3A3-070101.
• Engine and transmission repair coverage includes engine removal, reed-valve and top-end teardown, piston and crankshaft inspection, crankcase separation, bearing and oil-seal service, transmission and shift-fork work, clutch and primary-drive repair, kick-start service, reassembly, and final adjustment.
• Fuel, lubrication, and tune-up sections cover carburetor inspection and adjustment, float and cable settings, air-cleaner service, Autolube pump checks and bleeding, decarbonization criteria, ignition timing, and factory maintenance schedules.
• Chassis procedures address wheels, drum brakes, wheel-bearing replacement, rims and spokes, drive chain and sprockets, front-fork disassembly and oil-seal replacement, steering-head service, swingarm inspection, rear suspension, and control-cable maintenance.
• Electrical diagnosis distinguishes contact-breaker magneto systems from later CDI and J-model ignition-control circuits, with charging-output, coil, rectifier, condenser, lighting, and starting-interlock tests.
• Illustrations and technical data include major exploded assembly views, model-specific cable-routing drawings, five full-page wiring or circuit diagrams, torque tables, capacities, wear limits, clearances, adjustment data, and electrical test specifications.

How the Factory Books Work Together

This is a combined workshop reference, not a single standalone manual written from scratch for every motorcycle in the date span. Yamaha directs DT80J repair work to the DT80J/DT100J supplement together with the GT80E/GTMXE base manual and GT80G supplement. DT100J repair work uses the same J-model supplement with the DT100D base manual and DT100G supplement. The detailed teardown and repair chapters remain in the base books, while the G- and J-model publications supply revised maintenance, specification, chassis, and electrical information.

Coverage is limited to the exact models and starting numbers listed above. There is no GT80J section; the J-model 80cc publication in this set is for the DT80J. Factory tables distinguish the 2F4, 367, and 3J8 80cc-family builds from the 1T9 and 3A3 97cc engines. The 80cc drivetrain data covers four-speed transmissions, while the DT100 material covers five-speed units.

Repair and Diagnostic Depth

The engine chapters document removal, disassembly, inspection, repair, assembly, adjustment, and remounting. Internal coverage includes the cylinder head, cylinder, piston and rings, piston pin and bearing, crankshaft, crankcase, bearings and seals, clutch, primary drive, kick-starter mechanism, transmission shafts, shift cam, and shift forks. Carburetion sections add carburetor inspection and repair, reed-valve checks, throttle and clutch adjustment, and Autolube pump setup.

Factory tool references identify the flywheel holder 90890-01235, flywheel puller 90890-01189, clutch holding tool 90890-01022, crankcase separating tool 90890-01135, dial-gauge equipment, electrical testers, and dedicated front-fork oil-seal tools. The drawings include exploded views of the clutch and primary drive, transmission and shifter, carburetor, front and rear wheel/brake assemblies, front fork, and steering head.

The manual also flags repair traps that matter during a vintage rebuild. The crankcase section warns against forcing the case halves apart or striking the gasket surfaces, either of which can damage the machined joint faces. It also calls attention to shift-fork location and direction, while the DT100G material identifies the required clutch push-rod orientation; mixing these parts or positions can leave the transmission or clutch incorrectly assembled.

Electrical Systems and Shop Reference

Electrical coverage spans breaker-point ignition, CDI, charging and lighting circuits, and the DT80J/DT100J ignition-control unit with neutral- and sidestand-switch starting logic. A dedicated fault chart isolates no-start conditions in that interlock circuit. Full-page sheets cover the DT80J and DT100J wiring systems, the GT80E/GTMXE circuit, the DT100G wiring system, and the DT100D circuit, supported by ignition-circuit views and cable-routing diagrams.

Vintage motorcycle repair involves fuel, ignition, rotating-component, brake, and battery hazards. Use appropriate PPE, support the motorcycle securely, isolate electrical power where required, and follow normal shop fire-safety and ventilation procedures before teardown or testing.