1980 Yamaha XS850, XS850G, XS850SG Service & Repair Manual (P/N 3U8-28197-70)

• Covers the 1980 Yamaha XS850G and XS850SG, with starting serial numbers 3U8-000101 and 3V0-000101. The bilingual English/French file is a 246-page PDF carrying Yamaha document number 3U8-28197-70.
• Documents engine removal and remounting, top-end and cylinder-head repair, valve and camshaft work, cam-chain timing, crankcase and crankshaft inspection, oil-pump service, transmission overhaul, starter-clutch service, and clutch/primary-drive assembly.
• Includes Hitachi HSC34-II carburetor operation, disassembly, inspection, float and jet checks, diaphragm service, rack alignment, adjustment, and vacuum synchronization, with model-specific XS850G/XS850SG calibration data.
• Separates the G and SG chassis coverage, including model-specific front-wheel and axle layouts, the XS850SG front-caliper and slotted-disc arrangement, and distinct fork assemblies. Steering-head, swingarm, rear-shock, wheel-bearing, master-cylinder, caliper, and brake-bleeding work is also covered.
• Provides starting, charging, transistor-controlled ignition (TCI), lighting, reserve-lighting, self-canceling flasher, switch, and battery diagnosis, along with model- and region-specific wiring diagrams, component legends, and wire-color codes.
• Supplies factory special-tool numbers, torque tables, inspection limits, adjustment data, electrical test specifications, a lubrication/oil-cooler schematic, exploded assembly views, and XS850G cable-routing drawings. Internal final-drive overhaul and adjustment require the separate Yamaha Shaft Drive Service Manual.

Engine, Carburetion, and Drivetrain Repair Coverage

The engine chapter goes well beyond routine maintenance. Yamaha notes that the cylinder head, cylinder, and pistons can be removed without pulling the engine, while a separate engine-removal and remounting procedure supports crankcase, transmission, middle-gear, and full bottom-end repair. Inspection coverage spans the valves, guides and seats, springs and lifters, camshafts and timing components, cylinders, pistons and rings, crankshaft and connecting rods, and the transmission gears, shafts, forks, and shift drum. Assembly sections also address the trochoid oil pump, HY-VO primary chain, electric starter, starter clutch, and clutch damper.

The carburetion chapter explains the idle, main, and starter circuits of the three constant-velocity carburetors before moving into bench disassembly, fuel-passage and jet inspection, float setting, vacuum-piston and rubber-diaphragm checks, starter-plunger service, reassembly, and synchronization. Its specification pages distinguish the two model calibrations, including the Y-01 jet needle for the XS850G and Y-03 for the XS850SG.

Yamaha warns against casually separating the three-carb rack because the locked support plates establish carburetor alignment. The clutch-damper section likewise identifies spring damage from excessive press load and assembly damage if the damper pin and cam are not correctly aligned during circlip installation.

Chassis, Suspension, and Electrical Diagnosis

Chassis repair content is model-aware rather than generic. Separate illustrations and procedures cover the G/SG front-wheel and axle layouts, the different XS850SG front-caliper and pad arrangement, wheel-bearing replacement, front and rear master cylinders, caliper rebuilding, disc inspection, and hydraulic-system bleeding. Fork repair includes removal, disassembly, seal and component inspection, oil service, air-pressure adjustment, and left-to-right pressure matching. Rear-suspension coverage addresses spring preload and damping settings, supported by a load-based front-fork/rear-shock chart. Steering-head bearings, swingarm inspection and lubrication, rear-wheel and final-drive spline engagement, and universal-joint inspection receive their own service coverage.

Electrical repair begins with system-specific circuit diagrams, then supplies component tests and fault isolation for the starter motor and relay, AC generator, voltage regulator, rectifier, pickup coils, ignition coils, and TCI unit. The lighting chapter gives the reserve-lighting unit and self-canceling turn-signal system dedicated descriptions and checks rather than relying only on an overall wiring sheet. Appendix diagrams include the XS850G Canada wiring schematic, XS850SG Canada schematic, and XS850SG except-Canada schematic, each paired with a component key and color code.

Factory Data, Views, and Scope

Reference sections collect periodic maintenance and lubrication charts, component torque tables, clearances and wear limits, carburetor calibration, chassis settings, and electrical test data. Particularly useful illustrations include the carburetor exploded view and fuel-circuit diagrams, clutch-damper assembly, transmission and shift-mechanism layouts, model-specific brake and front-fork exploded views, the lubrication/oil-cooler schematic, and the two-page XS850G cable-routing layout.

Representative tool callouts include the tappet adjusting tool 90890-01245, vacuum gauge 90890-03094, clutch holding tool 90890-01228, damper compressor 90890-01250, final-gear lash tool 90890-01230, and electro tester 90890-03021. These references match the factory repair procedures to the intended holding, measuring, compressing, and electrical-test equipment.

The manual covers final-drive leakage inspection, lash checking, and driveshaft/universal-joint removal, inspection, and reinstallation. It does not contain the internal final-drive gear overhaul or adjustment procedure; Yamaha directs that work to the separate Shaft Drive Service Manual. For major repair work, the motorcycle must be securely supported, fork air pressure released before service, and brake fluid or fork oil kept away from painted and braking surfaces.