Fork Oil
Fork oil is specced from the Honda service manuals to be premium quality ATF(automatic transmission fluid) however, these days motorcycle-specific fork oils have improved drastically and are the go-to when replacing your fluid yearly or during a full fork rebuild. Replacing the fluid with a 10w (lighter rider) or 15w (heavier rider) motorcycle fork oil will help stiffen the front end slightly compared to the factory ATF(approximately 5w).
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Fork Oil Quantities for CT90 K1 - CT90 '79
Dry: 130 - 140cc (4.4 - 4.7 oz)
Refill after Draining: 120 - 130cc (4.1 - 4.4 oz)