Honda Trail CT90 S90 CL90L C90 CL90 CD90 1966-1977 Service Manual

Steve's Workshop's own family history lays out the shared-platform philosophy behind this entire lineup: "the S90 was the sports model of the range... the other 90cc bikes in Honda's line up included, the CT90, CL90, CD90 and of course the C90. All the bikes shared the same 90cc engine and similar transmission systems." This is precisely why Honda's own factory documentation bundles all five variants together — genuinely the same fundamental powerplant and transmission architecture, dressed in five very different bodies for five very different riders.

Power across the entire family comes from Honda's 89cc air-cooled OHC single, introduced in 1966 as a genuine engineering leap over the older pushrod OHV design used in the preceding CT200 and C105T Trail 55 — a lighter, more efficient valvetrain that Honda then applied consistently across every 90cc model in its lineup that year. The S90 ran this engine through a full 4-speed manual clutch transmission on a pressed-steel frame with telescopic front forks, rated at 8hp and claimed to cruise at 60mph on 18-inch wheels — genuinely the sportiest, most road-focused application of the shared architecture. The CL90 shared the S90's core mechanicals but was built for unpaved roads, running a higher exhaust line and 17-inch wheels with trail tires.

The CT90, by contrast, ran a slightly detuned version of the same engine paired with a genuinely different drivetrain: a semi-automatic centrifugal clutch (borrowed directly from the C90 Super Cub) mated to a 4-speed transmission and a manually-engaged 1.867:1 reduction gearbox, letting riders shift between road and low off-road ranges with a simple lever — freeing up the left hand, since the centrifugal clutch eliminated the need for a manual clutch lever, for an additional rear brake control. Steve's Workshop's own account calls the CT90 "a true utilitarian vehicle," with its low frame, under-seat fuel tank, trail tires, telescopic forks, and an auxiliary rear fuel tank and cargo rack (with optional passenger cushion) built specifically for genuine off-road exploration, camping, and hunting use. The CD90 filled yet another niche, replacing the older C200 as Honda's road-going commuter application of the same basic engine family.

Genuine mechanical evolution ran through the CT90 specifically across this span: 1966 launched with a cumbersome dual-sprocket low-range system requiring the rider to stop and manually clip an extra chain length onto a larger rear sprocket, replaced in August 1967 by the far more convenient posi-torque sub-transmission, letting riders switch ranges with a simple lever flip while idling in neutral. 1969 brought the CT90's most significant departure from its Super Cub roots — genuine telescoping front forks replacing the original leading-link suspension, along with broader chassis updates that made the Trail 90 a genuinely standalone platform rather than a modified city commuter. Because these five models share so much fundamental engine, transmission, and electrical architecture across this 1966-1977 span, Honda's own factory service literature treats them as a single documented family rather than five separate manuals.

This factory service manual covers the procedures, torque specs, and diagrams needed to keep a 1966-1977 CT90/S90/CL90/C90/CD90 running the way it was built to.