Honda 90 Series S90, CL90, CD90, C90, CT90 Shop Manual, 1977–Onwards (P/N 6220003)

• Coverage and document identity: Covers the Honda S90, CL90, CL90L, CD90, C90, and CT90 in a 186-page PDF. This is a Honda Motor Co., Ltd. Service Division factory publication, cover reference 6220003, copyrighted 1977 and printed in Japan.
• Engine repair scope: Documents engine removal and installation, cylinder-head and valve service, cylinder and piston inspection, cam-chain tensioner work, clutch service, oil-pump inspection, shift-mechanism repair, crankshaft checks, transmission teardown, crankcase service, kick-starter work, and carburetor adjustment.
• Model-specific drivetrains: Separates the manual-clutch S90/CL90/CL90L/CD90 from the automatic-clutch C90/CT90, the three-speed C90 from the four-speed models, and early CT90 dual-sprocket final drive from later Posi-Torque high/low range units.
• Chassis repair: Covers steering handle and stem, telescopic and bottom-link front suspension, fuel tank and frame body, brakes, front and rear wheels, rear fork, cushion dampers, muffler, air cleaner, and drive-chain service, with model-specific removal, inspection, and reassembly procedures.
• Tune-up and fault isolation: Includes compression checks, valve and ignition timing, breaker-point service, clutch and brake adjustment, carburetor tuning, battery and charging tests, scheduled maintenance, and symptom/cause/corrective-action charts.
• Electrical and illustration coverage: Provides model- and market-specific wiring diagrams plus power-flow, clutch, Posi-Torque, steering, suspension, wheel, and exploded component views.

Manual Contents

Honda states that the main text is based on the S90 and applies to the CL90, CL90L, CD90, C90, and CT90 unless a model-specific note says otherwise. Those notes matter: clutch actuation, transmission layout, front suspension, oil-pump construction, carburetor equipment, braking controls, and final-drive hardware vary across the series. This is a shop-service reference; its exploded illustrations identify assemblies and hardware but do not provide a complete replacement-parts catalog.

The engine chapters go well beyond routine maintenance. They cover disassembly and repair through the crankcases, valve-guide replacement and reaming, valve-seat refacing and lapping, cylinder and piston measurement, cam and rocker inspection, clutch-disc and spring checks, oil-pump testing, crankshaft runout, transmission clearances, and carburetor fuel-level and operating-range adjustments. Because this work calls for micrometers, dial gauges, spring testers, pullers, holders, and other specified tools, the overhaul material is suited to professional technicians and mechanically proficient owners; the routine inspection sections are less demanding.

Model and Production Differences

For the CT90, the manual documents the change from the removable dual-sprocket arrangement used through frame No. 122550 to the Posi-Torque subtransmission used from frame No. 122551 onward. It also covers the later 000001A-series, including its telescopic front fork and altitude-selector carburetor.

Separate supplements update the base manual for S90ZK1 and CT90K2-K6. They identify changes to the cam-chain tensioner, kick starter, carburetor, shock absorbers, axle hardware, air cleaner, handlebar clamp, crankcase protector, fuel sub-tank, brake wear indicators, switches, throttle control, and side stand. The CT90K8 ('77) supplement applies from engine No. CT90E-1800001 and frame No. CT90-1800001 and supplies its maintenance schedule, specifications, and wiring diagram. There is no separately labeled CT90K7 supplement in this publication.

Diagnostics, Diagrams, and Specifications

The troubleshooting section is organized by main-engine, carburetor, engine-noise, steering, clutch, gear-change, suspension, brake, and drive-chain complaints. A dedicated Service Tester Type ST 4B section covers continuity, resistance, condenser insulation, charging current, alternator output, ignition timing, ignition-coil performance, and engine-speed testing.

Named illustrations include the power-transmission diagram, manual and automatic clutch-mechanism views, CT90 Posi-Torque high- and low-range diagrams, steering-stem sectional diagrams, and front- and rear-wheel component views. The 6-volt electrical schematics are separately labeled for the S90 U.S. export, CL90/CL90L U.S. export, CD90, C90, CT90, and later CT90 000001A-series configurations. Factory data includes dimensional and performance tables, tightening specifications, clearances, wear and service limits, spring and damper test data, fluid capacities, carburetor settings, and electrical test values.

Factory Tools and Repair Cautions

The tool lists identify items such as dynamo rotor puller 07011-20001, valve lifter 07031-20001, oil-seal guide 07057-03301, clutch disassembly/assembly tool 07038-03301, rear-cushion tool 07035-03301, and front-fork oil-seal driver 07054-02801.

Honda specifically warns that installing the point base without oil-seal guide 07057-03301 can damage the camshaft oil seal and cause a leak. On S90, CL90, CL90L, and CD90 fuel tanks, using an overlength side-cover bolt can bottom against and puncture the tank. Wheel, fork, and brake work must be performed with the motorcycle securely supported as directed in the applicable procedure.