Honda NB50 Aero / NB50M 1983–1987 Service Manual Set + Provisional Info (P/N S0030)

Use the service edition that matches the scooter’s configuration when selecting inspection specifications and replacement components. The tool bulletin identifies required tools and approved alternatives.

The provisional booklet carries Honda’s instruction to discontinue its use once the shop manual became available.

Reading the PDFs and Wiring Diagrams

Search, navigation, and diagram detail: Neither PDF provides text search or embedded bookmarks. Small wire-color and connector labels in the checked wiring diagrams require zooming; each full wiring diagram is split across two PDF pages.

The ZIP contains two printable PDFs totaling 312 pages. The 174-page file combines the June 1983 manual, tool-bulletin copies, and provisional booklet; the 138-page file contains the December 1984 manual. The total already includes the four bulletin pages and eight provisional-information pages, including the booklet’s cover.

Two-Stroke Engine, Automatic Drive, and Electrical Service

The following selected coverage highlights outline the main repair areas. Other included topics include cable and harness routing and fuel-tank removal.

• Engine repair: Step-by-step engine removal and installation, cylinder-head/cylinder/piston service, crankcase separation, and crankshaft bearing replacement.

• Automatic transmission: Drive and driven pulley disassembly, weight-roller inspection, centrifugal clutch repair, and final reduction overhaul.

• Carburetor service: Float and jet inspection, reed valve checks, auto-bystarter testing, and vacuum-operated fuel valve diagnosis.

• Oil injection: Pump removal, external inspection, and bleeding, plus control-cable adjustment on the early configuration.

• Brakes and chassis: Drum brake service, wheel bearing replacement, steering-head bearings and races, and front and rear suspension disassembly.

• Electrical diagnosis: CDI ignition, charging faults, starter operation, and lighting, supported by wiring diagrams and switch-continuity charts.

The repair procedures suit mechanically experienced readers with precision measuring equipment and the specified service tools; Honda identifies only selected maintenance tasks as owner-serviceable.

Configuration Differences Between Editions

The early configuration combines a PA 05A carburetor, leading-link front suspension, electric and kick starting, and a battery with removable cell caps. The December 1984 edition covers a PA04G carburetor, trailing-link front suspension, electric starting, and a sealed battery.

The editions also use different bore/stroke dimensions and transmission ratios. The early manual has 17 chapters, including Technical Features; the later manual has 16 chapters and a separate Frame Covers section.

Engine, Fuel System, and Drivetrain Repair

Cylinder-head, cylinder, and piston work can be performed with the engine in the frame; crankshaft service requires engine removal. The engine sections address A/B cylinder identification, connecting-rod clearances, and crankshaft runout.

Factory assembly notes explain how piston rings riding over their locating pins can break and damage the piston and cylinder.

Auto-bystarter testing includes electrical resistance checks and pressure checks of the enrichment circuit. The early manual’s Auto-Bystarter cutaway and operating chart explain the PTC heater, thermo-wax, diaphragm, and metering needle. Its Oil Pump Performance Curves relate oil delivery to control-lever position.

Oil pump service stops at inspection and replacement; Honda expressly prohibits internal pump disassembly. The lubrication warnings explain that trapped air can interrupt oil delivery and cause severe engine damage.

Drivetrain troubleshooting distinguishes a running engine with no vehicle movement from clutch drag, weak acceleration, and abnormal pulley noise. The later edition also documents driven-pulley bearing replacement and starter pinion inspection.

Electrical Diagnosis and Factory Reference Data

The Charging Circuit, Ignition Circuit, and Starter Circuit diagrams trace the components involved in charging, spark, and cranking faults. Separate diagnostic charts address low-oil indication and fuel-gauge behavior.

CDI resistance tables identify the required tester models and measuring ranges, since an unsuitable meter can produce misleading results. Ignition timing coverage is inspection-based: the CDI timing is not adjustable.

The early manual covers starter motor disassembly, brush and commutator inspection, and reassembly. The later edition covers motor removal, operational testing, and installation.

Factory reference data includes component-specific torque tables, fluid capacities, piston-to-cylinder and bearing clearances, wear limits, carburetor float settings, and electrical test values. Tool tables identify applications and U.S. alternatives, including clutch spring compressor 07960-KJ90000 and case puller 07935-KG80000 for clutch and crankcase work.

Have brake and suspension repairs checked by a qualified technician before riding.

Selected Piston Clearance and Drive-Belt Inspection Values

Both service editions list a standard cylinder-to-piston clearance of 0.035–0.050 mm and a 0.10 mm service limit, alongside the related piston, cylinder, and pin measurements.

Drive-belt width service limits differ: 12.5 mm in the June 1983 manual and 14.0 mm in the December 1984 manual. Each pulley section pairs its limit with inspection procedures.