In this article I will briefly familiarize you with the original equipment (o.e.) Kawasaki/Suzuki 65cc suspension design, tuning tips, and modifications. As a suspension tuner and motocross hobbyist I have observed a lot of discussion over o.e. KX/RM65 suspension. There are numerous message boards filled with ambiguous suspension modifications and specifications for this motorcycle.
The front forks on the KX/RM65 are outdated by several decades but can be adjusted for certain riding conditions. Damper rod forks as found on KX/RM65s are outdated since they create an overly progressive dampening curve (they are too soft initially and too harsh during fast fork movement). The rebound adjuster on the front forks can be used to adjust for some cases of head shake and cornering difficulties. Head shake may occur it can due to too much or to little rebound dampening. This may be fixed by turning the adjuster in increments of two clicks and test. The rebound adjustment can also aid with cornering problems. If the bike washes out in corners, turn the rebound adjuster clockwise in increments of two clicks. If the bike does not stand back up from corners fast enough, turn the rebound adjuster out in increments of two clicks. The front of the bike can also be lowered by moving the forks up in the triple clamps. This may aid in cornering but can cause head shake.
The KX/RM65 models are equipped with a rebuildable rear shock that is mounted to a modern linkage system. This system increases the shocks work load as the rear suspension compresses further towards bottoming. A starting point to adjusting the rear shock is to set race sag at 70-75mm but to not exceed static sag by 25mm. If meeting the two conditions is not feasible, a different rate shock spring may be needed. The rebound adjuster can aid rear end stability and traction. If the rear of the bike swaps to the sides or kicks up it may be due to too much or lack of rebound dampening. To solve this turn the rebound adjuster in increments of one turn and test. Rear traction is often times lost when there is too much rebound dampening and this may be solved by turning the rebound adjuster counter clockwise one turn.
The o.e. KX/RM65 suspension performance does not suffice most competitive motocross riders. There are two effective popular tuning services available for the KX/RM65 forks. An emulator valve can be installed which offers a less progressive and more predictable feel to the front end of the bike. This mod is sold as a “bolt on kit” but is not effective if installed in that fashion. Additional damper rod modifications are needed to tune rebound dampening properly. A cartridge system is also available for the forks that can be installed after machining of the lower fork legs. This cartridge system can be tuned by replacing shims and via rebound and compression adjustments. The o.e. KX/RM65 rear shock has a lot of potential and can be tuned by a revalve service. The KX/RM65 suspension may be mediocre initially, but with proper suspension tuning services it can become a very competitive 65cc dirt bike.