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

The Dr. Pulley clutch was chosen for its wide range of adjustability and the ability to raise the engagement speed without increasing slip.

After some research, we decided to try the Dr. Pulley Clutch. Prior experimentation had been done by Battlescooter with the KN Kikaku clutch but the test bikes lost top speed. We theorize that this was because when stiffer clutch springs were used to improve launch, the stockish Ruckuses that were used for testing didn’t have enough revs to fully lock the clutch and top end slippage resulted. We knew that we would need a lot of tuning flexibility so we selected the Dr Pulley clutch as this is the most adjustable clutch on the market.

We used a 50cc GY6 clutch bell as it has the larger 107mm Dr. Pulley Clutch diameter with the same pinion shaft splines as the Ruckus.  We machined 0.100" off the center post where the pinion shaft slides in to get the bell to sit more inboard so all of the clutches shoes would contact the bell.  You don't have to do this but the clutch will work slightly better and possibly last longer if you do.

The Dr. Pulley clutch is awesome because you can adjust the stall speed of the clutch via the centrifugal springs on the shoes. These control the clutch's engagement RPM. We wanted to raise the launch rpm to make up for the sluggishness caused by the higher gear ratio. This would get our Ruckus moving right as the engine was getting into its powerband. What makes the Dr. Pulley so cool is that it can totally lock up solidly even with a high engagement speed. With other race clutches, when stiff springs are used to raise the launch RPM, the clutch loses centrifugal locking force. This makes them slip more, not exactly a combo for good top speed or acceleration. Dr. Pulley clutches have a cam wedging device that mechanically locks the clutch shoes on the drum once they are engaged by using the engine's torque driving force to help lock the clutch. Thus the Dr. Pulley is the only clutch that can have both a high launch RPM and a solid top end lock up.

The Dr. Pulley clutch on the left has shoes much bigger than stock stock clutch on the right.  Plus there are three of them vs the stock two.  The friction material is also a more performance oriented semi metallic material vs the stock cardboard like stuff that the stock clutch uses thats designed more for smoothness.  As you can see the stock clutch is all glazed from slipping with our powerful modded engine.  The Dr. Pulley clutch is bolted to a Yamaha Jog/Zuma contra pulley to make it work with our Ruckus.

The rpm at which lock up occurs and how hard the clutch locks up is adjusted using an additional set of springs called pillow springs. The pillow springs counter the engine's torque and reduce the cam wedging action. The stiffer the pillow springs, the higher the lock up rpm and the smoother the lock up will be. The Dr. Pulley clutch has a much more durable semi metallic friction material as opposed to the cardboard like stock stuff. It also has 3 shoes as opposed to the stock two and has about 3 times more shoe area that stock. This clutch will probably last forever on a Ruckus!

To help tune the transmission, we used a Malossi red high tension contra spring from a Yamaha Zuma to slow upshifting.  This keeps our cammed out modded engine in the powerband better, reduces belt slip and lets the transmission downshift better on the hills. We also used a Malossi torsion controller bearing from a Zuma which helps smooth out transmission operation.  To install the contra spring is a two guy operation, one person has to compress the spring while the other tightens the lock nut down with an impact.

Unfortunately Dr. Pulley does not make a direct bolt in clutch for the Ruckus so we had to use some parts swapping trickery to use a common Minarelli Dr. Pulley clutch on our Honda. This is the same clutch used for a Yamaha Jog or Zuma so these tricks can be used to adopt any performance clutch for these scooters, like a Polini or a Malossi although we think the Dr. Pulley clutch works the best. We obtained our Dr. Pulley stuff from Vince at Scooter Dynasty who was very helpful in contrast to the distributer MRP who hung up on us. Vince got us our parts quickly and at a good price.

To tune the Dr. Pulley clutch to the high revving characteristics of our built engine, we went up two stiffness levels in clutch spring stiffness to raise the launch rpm.  We also removed the pillow springs as shown here to get maximum lock up.