One of the big challenges a custom builder faces is keeping the bike he or she is building clean. Each component added to a bike creates a potential eyesore; none is worse than a throttle cable flopping around the right side of your bike. There is no question that an internal throttle cable is clean, but not everyone knows how to install one. We happened to be at Jim Nasi Customs in Scottsdale, Arizona, as the staff was prepping a bike for such an install. Nasi and his crew specialize in building custom handlebars with internal throttles, so getting them to go through the steps involved for us was easy.
In order to have even grip spacing, the bar needs to be cut short on the throttle side. A good, sharp pipe cutter makes the process shorter for fabricator John Beckwith. | 
Now it is necessary to reassemble the twist assembly and measure the distance to the set screw. | 
The distance is marked on the bars and the set screw hole is drilled. Beckwith then drills four more holes 1-inch farther down toward the end of the bar. These holes will be welded to the internal twist piece to secure the throttle to the bars. |
Next, the set screw is installed with some Loctite on the threads. | 
Look closely at this picture taken immediately after the holes were welded up, and you can see smoke coming out of the bars. | 
We jump ahead here. The bars are mounted onto the triple tree, and a small-diameter wire is fed through them to a pre-drilled opening at the bottom of the riser. Next, one end of the included cable is clipped off. The cable is taped to the end of the wire and is pulled through the bars. |
If this bike were ready to be assembled and not a bare chassis, the cable would be run to the carburetor to get an idea of the amount of trimming necessary. | 
Beckwith has done enough of these assemblies to know how much casing will be clipped off. He also marks a spot on the casing where the next set screw will go. | 
The larger fitting clamps onto the cable to move it when the throttle is twisted. The smaller piece simply positions the larger one against the casing. |
Now a slide pin is installed into the inner twist piece. The pin connects the throttle assembly pieces via a channel cut inside the outer grip and pulls the cable as the throttle is twisted. | 
With grips and controls in place, you start to see how clean this idea can be. For those adventurous types, you can take things a step further by routing the cable through the frame and dropping it out just above the carburetor. |  |