1977–1982 Honda NC50 Express / NA50 Express II Factory Service Manual (P/N AH22008109C)

• Covers the 1977-1982 Honda NC50 Express and 1979-1981 Honda NA50 Express II in Honda shop manual P/N AH22008109C, combining the base NC50 sections with the included '79 NA50, '80 NC50, '80 NA50, '81 NC50/NA50, and '82 NC50 addenda.
• Covers engine removal, cylinder-head/cylinder/piston repair, oil-pump service and bleeding/priming, A.C. generator work, spring-starter and kick-starter repair, clutch/final-drive service, crankcase/crankshaft inspection, and carburetor disassembly and testing.
• Separates early breaker-point ignition from later CDI diagnosis and documents the 1981 automatic choke and NA50 two-speed automatic transmission, including first- and second-gear operating diagrams.
• Includes wheel, brake, front-fork, and rear-shock procedures, cable and fuel-line routing, troubleshooting charts, special-tool data, component-location views, and model-specific wiring diagrams.

Mechanical and Electrical Documentation

This factory publication is organized around the original NC50 technical features and repair sections, followed by model-year addenda for the later machines. The early NC50 specification pages distinguish 1977 and 1978 engine and spark-plug data rather than treating both years as one unchanged build. The 1979 NA50 material adds its own engine-removal layout, under-seat fuel/oil filler and electrical layout, seat and rear-shock work, cable routing, and wiring. For 1980, the NC50 electrical section separates U.S. and Canadian turn-signal and condenser configurations, while the NA50 receives its own routing, specification, and wiring updates.

The combined 1981 addendum documents the change to capacitor-discharge ignition, an automatic-choke system, and a kick-starter system for the NC50 and NA50. It explains the NA50 two-speed transmission as a compact assembly of two centrifugal clutches, a ratcheting one-way clutch, and a planetary gearset. The 1982 NC50 addendum updates the front-fork/front-wheel data and records a higher front-axle nut torque. It also covers the fuel tank, seat, rear carrier, charging-system tests, cable and fuel-line routing, a changed fuel-filter maintenance interval, updated specifications, and a dedicated wiring diagram. Each addendum refers back to the base NC50 procedures for unchanged work; the PDF keeps those base sections and all five listed addenda together.

Engine coverage begins with the 49cc air-cooled two-stroke design, including dual reed valves, three-port Schnuerle loop scavenging, the piston-type carburetor, and the crankshaft-driven plunger oil pump. The technical-feature pages trace power from the starter drive and chain through the automatic centrifugal wet clutch, drive chain, helical final gears, and rear wheel. Repair chapters cover engine removal and installation, cylinder-head decarbonizing, and piston, ring, pin, and cylinder inspection. Further sections handle oil-pump removal and leak checks, pump bleeding and priming, A.C. generator removal, early-model ignition timing, left-cover/starter work, clutch and drive-plate removal, final-drive and bearing inspection, crankcase separation, crankshaft and connecting-rod checks, and carburetor overhaul. The manual specifically states that all engine service except crankshaft work can be performed with the engine in the frame.

Chassis repair includes handlebar and steering-head work, ball-race removal and installation, the telescopic front fork, and front and rear wheel hubs. It also covers spoke and axle inspection, drum-brake repair and brake-arm resetting, rear shock absorber disassembly, and fuel/oil tank, seat, and rear-carrier work. The special-tool pages identify the flywheel holder (07925-0010001), pin spanner (07916-0440000), case pullers (07933-1470000 and 07935-1870000), clutch pullers (07935-8050000 and 07935-1470001), oil-seal assembling tools (07953-1470000 and 07965-1480001), and rear shock absorber compressor (07959-3290000).

Technical Preview and Specifications

Electrical coverage follows the production changes instead of applying one test routine to every year. Early models use breaker points, a condenser, ignition coil, A.C. generator, rectifier, and battery. The 1981 and 1982 sections add CDI component locations, ignition-circuit inspection, ignition-coil and generator resistance tests, CDI terminal test charts, charging-output and rectifier checks, switch-continuity data, and lighting, horn, stoplight, and turn-signal diagnosis. The CDI-era inspection section also directs replacement of the stator coil and flywheel as a matched set rather than replacing only one component.

Named illustrations include NC50 Two-Stroke Port and Valve Timing, NC50 Scavenging, Power Transmitting System, Lubricating Oil Flow, Automatic Choke Operation, and How the Transmission Works in 1st Gear/2nd Gear. Supporting drawings include exploded assemblies, cable and wire-harness routing views, fuel-line routing, and component-location layouts. Wiring diagrams are separated for the base NC50, 1979 and 1980 NA50, 1980 U.S. and Canadian NC50, 1981 NC50/NA50, and 1982 NC50.

The stored-energy starter is a real repair trap. The manual requires the spring to be fully released before left-cover, starter, or top-end work and identifies the spring/sustaining-plate unit as an assembly that must not be taken apart. Starter-sprocket punch-mark indexing must also be preserved, and the crankcase mating surfaces must not be scratched because the two-stroke crankcase has to remain pressure-tight. On 1981 models, the automatic-choke control box is not to be disassembled, and a replacement cylinder must carry the same A or B code as the original.

Factory reference data includes component-specific torque tables, assembly clearances, wear and repair limits, electrical test specifications, maintenance schedules, and troubleshooting tables. Fault-finding covers no-start and starts-then-stops conditions, power loss and overheating, starter and clutch faults, weak or missing spark, heavy steering, poor braking, and drivetrain noise. Observe the publication's safety precautions when working around the stored starter spring, fuel, battery electrolyte and hydrogen gas, high-tension ignition, and rotating drivetrain parts.