1     5/16 x 1/2 UNC stainless cap screw
1     8-32 x 2 stainless machine screw
1     knob with 8-32 internal thread
1     1/4 x 1 x .035 spring
1     8-32 nylon cap nut
2    #8 flat washers
1    #8 spring or rubber washer
1     8-32 nut
 

You will need a 5/16 UNC tap and drill (F bit: .2570") to install.

OK now here are the steps:

1) Remove the forward half of the throttle housing. I'm not going into describing that, you have to figure that out yourself.

 2) Next you need to drill out the hole for the cable retaining screw with the appropriate size drill (F bit) and tap the hole with 5/16- UNC threads. This needs to be done because the existing hole is too small for the control to go through.

 3) Drill out the hole in the cable retainer with a 5/16 drill.

 4) Check the throttle grip assembly for any rough edges on the black plastic where the cables attach. The friction device rides on the black band. Mine had a mold mark that was easily sanded off. If you don't it will make for a rough throttle.

 5) Test assemble the parts as follows:
put a flat washer on the knob followed by the spring
thread this into the cap screw
thread the cap screw into the throttle housing
thread the 8-32 nut onto the screw inside the throttle housing
put the spring washer on the screw
put a flat washer on the screw
put the nylon nut on the screw (note: it has no threads so it should just slide on)

At this point you may have to dremel out the throttle housing some to get some clearance. You will also have to determine how long the spring should be to prevent binding. (GZ: I have already trimmed to a rough length but you may have to clip it slightly to fit your application.)

Once you are certain all is well, it is time to install it on the bike.

6) Attach the throttle cable back onto the housing using the 5/16 cap screw and tighten.

7) Thread the knob into the housing with the spring and washer on it.

8) Thread the nut onto the screw.

9) Put a flat washer on and then the nylon nut. Wind the nut onto the screw far enough that there is a gap between the nut and the nylon nut. Drop a drop of Locktite in the gap and then wind the nut back up until it just touches the nylon nut. Note: you want the nut glued to the screw so that it pushes up on the nylon nut through the spring washer. This gives adequate range of adjustment. I tried it by just having the screw push on the nylon and it resulted in a workable but touchy adjustment. Remove the nylon nut and flat washer and go have a beer while the Locktite dries.

10) Now put the spring washer on the screw followed by a flat washer and the nylon nut.

11) Carefully reassemble the throttle housing without dropping the nylon nut and washers out.

There you have it. Now you tighten the knob until the nylon nut applies friction to the throttle.

Note: This device can be a safety issue for inexperienced riders since the throttle will no longer return when you release it. You have to twist it to idle to slow down. While getting used to it I would suggest only tightening the knob while cruising and loosening it in stop and go situations.