Project Honda Ruckus Part 6: The Final Option, Tuning the Transmission


We removed the entire stock Honda clutch and contra pulley and replaced it with the Dr. Pulley clutch and Contra pulley from a Zuma/Jog. As the Dr. Pulley clutch is bigger in diameter than stock, we had to use a clutch bell from a 139QMB scooter which uses the small 50cc GY6 engine. This bell has the larger 107mm diameter of the Dr. Pulley clutch but the same pinion shaft splines as the Ruckus. We machined 0.080″ off of the mounting boss of the bell so it would line up perfectly with the clutch shoes. This isn’t absolutely needed but we wanted to use every bit of the clutch shoe engagement.

Honda Ruckus Dr Pulley Clutch washer spacer
When installing the Dr. Pulley clutch, you have to add a spacer to the pinion shaft or the Jog contra pulley will bottom out on the transmission case and get bent when you tighten the nut.  Don’t bother to call MRP about this problem, they don’t show you this in their tech video and they will hang up on you if you call!  We ground down three washers to fit inside the contra pulley without rubbing to act like spacers so the pulley could spin freely without hitting the tranny case.

When installing the Zuma/Jog Dr. Pulley clutch you have to shim the pinion shaft to prevent the contra pulley from hitting the gear case. We used three washers and ground the ID to fit inside the contra pulley. Later Scooter Dynasty came out with a nice spacer to make this easier so if you order this clutch, be sure and get the spacer.

When testing the clutch we could immediately see that this had a lot of potential as all slip was eliminated and the launch speed was raised slightly. However, we still had to do more tuning. The Dr. Pulley clutch comes with a big assortment of springs for tuning the launch and lock up rpm. The clutch is shipped with the softest blue spring in place. This spring started to engage at 5000 rpm, and grabbed at 6500 rpm. We needed more to get the engine into its powerband and opted for two steps stiffer, the yellow spring. This spring started to engage at 5800 rpm, and grab hard at around 7500 rpm. We also removed the pillow or lock up spring entirely for the hardest lock possible.

Scooter dynasty dr pulley clutch adaptor spacer for honda ruckus
Later we got this spacer that Scooter Dynasty had made to do the job correctly.  This spacer is pretty easy to make but it’s cheap and easier just to buy it.

This made a big difference, launching our Ruckus hard out of the hole and moving down the street while still maintaining street drivability. This got us about half of our acceleration back. We still felt that the combination had issues; the transmission shifted up too aggressively and didn’t respond well to hills. Our engine once launched, was held at too low of an rpm, right when the engine was starting to come into its powerband but still at slightly too low of an rpm for optimal acceleration. We needed to make the variator more sensitive to load and to make the upshifting curve better match the higher rpm biased characteristics of our modified engine.

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