Yamaha CA50K / Riva 50 Factory Service Manual 1983–1986 (P/N LIT-11616-03-64)

• Coverage and document identity: A 164-page PDF of the Yamaha CA50K Service Manual, model code 20G, beginning with federal VIN *JYA14T00DC200101 and engine number 14T-200101; Yamaha P/N LIT-11616-03-64**, first edition, July 1982.
• Engine overhaul coverage includes engine removal and mounting, cylinder-head and cylinder service, piston and ring inspection, crankcase splitting, crankshaft installation, transmission work, and final assembly checks.
• V-belt drive and starting-system service covers the primary and secondary sheaves, automatic centrifugal clutch, V-belt, kick starter, electric starter, starter clutch, C.D.I. magneto, and Yamaha Autolube pump.
• Carburetion and intake procedures take the Y12P-5A TK-KIKAKI carburetor through removal, disassembly, inspection, assembly, adjustment, and installation, with separate reed-valve and B.V.S. auto-choke coverage.
• Chassis repair sections address front and rear wheel removal, drum-brake disassembly and inspection, meter-gear service, front-fork work, steering-head bearing service, rear-shock inspection, and control-cable maintenance.
• Electrical and visual references include starter, charging, and ignition troubleshooting charts; lighting and signal-system test procedures; a color CA50K wiring diagram; a 15-page exploded-diagram section; and factory torque, capacity, clearance, wear-limit, and electrical-test data.

This factory service manual is built for maintenance, diagnosis, and repair beyond the scope of an owner’s handbook. Yamaha wrote it primarily for dealers and qualified mechanics, and it assumes a working knowledge of motorcycle repair concepts and procedures.

Engine, Drive, and Fuel-System Detail

The engine chapter distinguishes components that can be serviced with the powerplant still in the chassis from work that requires complete engine removal. Inspection coverage includes the cylinder head, cylinder bore, piston and rings, crankshaft, bearings, clutch shoes, sheaves, V-belt, starter parts, transmission gears and axles, and Autolube drive components. Reassembly sections add gasket and seal practices, bearing and circlip orientation, crankcase sealing, component-specific torque specifications, and lubrication points.

The V-belt overview explains how centrifugal weights move the primary sliding sheave as speed rises, while the secondary sheave’s helical splines convert transmitted torque into thrust to increase the reduction ratio under load. That operating theory helps connect belt, sheave, spring, and clutch symptoms to the parts inspected later in the repair chapter.

Carburetion material goes well beyond jet specifications. A labeled section view traces the air, fuel, and mixture paths through the carburetor, followed by float-valve, jet, passage, diaphragm, needle, throttle-valve, float-height, and fuel-level checks. The auto-choke diagrams show how the temperature-sensitive B.V.S. valve, vacuum-operated fuel cock, and carburetor choke valve interact during cold starting, partial warm-up, full warm operation, and restarting. Reed-valve inspection and installation are covered separately.

Chassis and Electrical Diagnosis

Front and rear brake sections pair disassembly drawings with drum inspection, shoe-lining wear limits, camshaft and indicator-plate alignment, reassembly, and brake-lever adjustment. Wheel-bearing checks, axle-bend and wheel-runout inspection, bottom-link front-fork service, steering-head bearing adjustment, rear-shock inspection, and cable-routing guidance round out the chassis repair coverage.

Electrical diagnosis is divided into the starter, charging, ignition, lighting, and signal systems. The manual supplies circuit-specific diagrams and test data for the starter relay and control unit, starter-motor brushes and armature, battery and rectifier, C.D.I. magneto and ignition coil, A.C. regulator, horn, oil-level switch, fuel sender, flasher relay, and handlebar switches. Ignition timing is identified as factory-set, so the manual provides the benchmark but no timing-adjustment procedure. The battery is the specified 6V 8AH unit, with charging, specific-gravity, and breather-hose inspection information.

Tools, Diagrams, and Repair Cautions

Factory tool references include the sheave holder YU-01701, crankcase separator YU-01135, crankshaft installation set YU-90050/YU-90063, flywheel puller YM-01189, clutch-removing tools YS-28891/YM-04045A, and Yamaha Pocket Tester YU-03112. These references matter when planning a crankshaft, clutch, magneto, or electrical repair before disassembly begins.

Named exploded views include Crankshaft and Crankcase, Sheave, Clutch and V-Belt, Carburetor, Front Wheel, Steering Head and Handlebars, and Electrical Components. Separate cable-routing sheets and the full color-coded wiring diagram show physical routing and circuit relationships that are difficult to infer from prose alone.

The manual repeatedly warns against getting oil or grease on the V-belt, sheave faces, clutch housing, or clutch linings, because contamination can damage the belt and friction surfaces and disrupt drive operation. During top-end assembly, incorrect piston direction or ring-gap placement can damage the piston rings as the cylinder is installed. Battery charging must be performed with ventilation and away from flame or sparks; the electrolyte contains sulfuric acid and requires appropriate eye and skin protection.