The internal throttle installation process is pretty straight forward, but can become a little confusing, especially for a first timer. The instructions most of them include are a little vague, and miss some of the finer points. We will go through the steps needed to do a proper throttle install in two segments. Part 1 covered the throttle itself and part 2 will cover making and installing a throttle cable. When done properly, an internal throttle can really clean up a set of handlebars, and in turn, the bike it is mounted on.
The first step to installing the cable on your internal throttle is to gather up the parts and tools you’ll need to get the job done. Here is a shot of what I normally use when I do this job.
The Internal Throttle:
Allen Wrench set
Lineman pliers (or some other sharp cutter... angle grinder with a cutoff wheel also works if you’re safe). Not shown here, but also used, is a small belt sander to de-burr the cable after you cut it. And, of course, some Blue Thread locker.
The throttle cable I now use most often is a Barnett product specifically for doing internal throttle cables. It comes with the carburetor end of the cable pre-made, a cable adjuster that sits right above the carburetor and an excess of cable and housing to trim to fit.
This is by far the easiest and time-saving way to do this job. That being said, there are other ways to make your cable. I’ve used other types of “build your own” cable kits, as well as taking old throttle cables and basically making the Barnett set up by cutting and splicing them together. Now that I charge by the hour, getting the job done right and as fast as quality allows is the goal, so the Barnett cable seems like a no-brainer.
I will say that using the Magnum “Build your own” cable kit will give you one other option. What I do if I use that cable kit is get the 96’ and later, 90 degree kit and flip it around so that the 90 degree end that normally goes into the throttle housing is at the carburetor side. I also have to make an adaptor to fit the cable end into the throttle stop ferrule on the carburetor when I use this method, but overall it results in a nice look. (It also requires some tweaking of the bend to clear the front head, etc.) Because of this, and because of the extra time this way takes, I normally use the Barnett cable.
So, we left off last time with the Throttle itself installed into your bars. (In that How-To, I outlined using thread locker on some of the setscrews. Since, in reality, you would be doing this whole job all at once, you don’t need to use any thread locker on the install of the throttle until you’ve got the cable made up too. This is because to make the cable, you have to take the throttle on and off a few times.)
The first step in getting the cable made up is to install it into the carburetor and route it up to the bars how you’d like it.
I like do all this figuring with the bike on the ground, so I can account for how the cable lays as the front end turns from side to side. You’ll have to guess a little at first, but you’ll be able to check this as you go along.
Once you see how you want the cable to run up from the carb to the bars, drill a hole in the bars for the cable to enter the bars. It’s nice if you can ream the hole a bit to allow the hole to have a similar angle to the angle that the cable will be entering it. (stop giggling and keep working)
Once you have the hole set, chase the cable through your bars. This will be met with varying levels of difficulty, so plan accordingly. The Farrier bars we are using on the Shop Sporty are nice and smooth inside so this was an easy job.
Once you have the cable in the bars, you can spend some time really dialing in how you want the cable to run. Take your time and make it look good, and also make sure it doesn’t get pinched or bind up anywhere. I decided to add a P-clamp to one of my tank mounts to keep the cable in place as it’s a bit cleaner looking than a wire tie. This is also a good time to swing that front end back and forth and make sure you’re leaving enough slack in the line.
One thing to be cautious of as you’re prepping the cable is to make sure that the cable does not pop-out of the adjuster. It can do this because there is no tension inside the housing yet. You can throw a piece of tape on it if you like, or just keep an eye on it. If you don’t, and you start making the measurements in the next few steps, you will have to go back and re-do them…. if you haven’t already cut the cable too short.
So, the next step is to determine the length of the housing. To do this, first make a few measurement marks to see where the throttle components actually sit when in-place in the bar.
Here you can see where the cable housing-stop sits inside the bars. At this point, if your cable is run the way you want it, mark it right where it exits the bar as a reference point and then measure back to where the cable housing will sit inside the housing-stop.
In this picture, you can see that I need to cut the cable BACK approximately 1.5” from the mark that references the end of the bar. Next, slide the cable out of the bar and mark that on the housing itself. I like using tape on the housing and not silver sharpie because it won’t wipe off and it’s easy to see if something looks wrong.
Once you’re sure you like the measurements, you can cut the housing. Make sure that you either pull the inner cable BACK or take it totally out before you cut the outer housing! The housing will cut easily with a sharp set up side cuts, lineman’s, etc. I always cut it a hair on the long side, just to be safe.
Depending on how you cut the cable, you may need to clean up the end a bit. A quick trip to the sander will suffice. Also, take a small pick and make sure the center of the housing is free of any debris or burrs.
Once the end of the cable is set, chase it back into the bars and go dig into the parts you have left over from the internal throttle box. In it, you should have 1 allen set screw that is smaller than the rest.
This is the set screw you will use to lock the outer cable housing into the stop. Grab some thread locker and put the assembly together as shown.
You don’t need to crank the piss out of that tiny set screw, but make sure it’s good and snug. Once everything is all together, and if you’ve routed your cable properly, the housing should never really get pulled “backwards,” thus the chances of it popping out are slim. Another way to say this is that the tension inside the system is pulling it together, not apart.
In the last picture you’ll also see that I pushed the inner cable back through the housing. We now need to determine where to cut this cable. To do this, we want to approach it the same way we did the outer housing.
First we want to know how much free length the cable needs to reach the spot it gets locked into the “Cable sled.” Take your throttle and measure how far in the sled sits when the throttle is in the “resting position.” That is, where it will sit when not being twisted.
As opposed to where it sits when fully twisted.
The distance the sled is at in the first photo, its resting position, is the dimension you want to know. Take a set of calipers, or a depth gauge, or slide a section of the cut off housing into the throttle and mark a part to determine this measurement.
Once you have that number, you can lay it out on the cable as shown.
Remember that the outer cable housing has an adjuster in it. This allows you to make the length of the cable housing LONGER. So when you lay out your cut line on the inner cable, you can also err on the side of safety and make it a hair long, because you’ll be able to take up the slack when you adjust the cable housing. This will also allow for the part of the cable that slides into the cable sled and gets locked down by the set screw. (approximately ¼”)
Once I’ve made this cut, I like to make a dry run (without locktight) of the remaining steps, to make sure all my cable lengths are going to work together. So, assume from this point on that I’ve actually lightly assembled this once and made sure it all works, that I have enough adjustment in the housing, and that the throttle works as it should.
Once you confirm all that, disassemble back to this point and now, using thread locker on the cable setscrew, lock the cable in. This setscrew you DO want to make as tight as you can without stripping the allen. Really crush the cable in there. The security of this connection is critical because it is ALWAYS under a force that wants to pull it apart when it is in use. I’ve never had an issue with the cable pulling out, but I make sure to get this connection as tight as I can, and I also like to use thread-locker liberally here. Let some of it get into the cable areas as well, it can’t hurt.
Once you’ve done that, slide the cable sled into the throttle body and put the little bearing back into the cable sled.
Then, slide the outer sleeve back on the throttle, (put some thread locker on the allen screw in the end of the throttle that holds the outer sleeve to the inner tube) and install the assembly into your bars, using thread locker on the set screws that hold the throttle into the bars as well.
The last step is to take out the slack in the cable housing. Be careful not to remove too much however, or you’ll artificially bump your idle speed. You want to just take out the majority of the “slop”. The exact setting is really a matter of preference and you can play around with it.
If you’ve done everything right, you should have a nice, smooth throttle! It’s a little hard to twist without the extra leverage you get with a grip installed, but here you can see how everything works.
The only thing you’ll still need to do is install whatever grips you choose. Don’t forget that because you’re not using a normal throttle sleeve, the outside diameter of both bar ends is the same. This means you’ll need TWO sets of grips, because the grip with the large bore for a traditional throttle sleeve will be too loose on the bar to work properly or safely. Here we see the finished assembly on the Shop Sporty. Nice and clean!
As always, thanks for the support and of course, Chop on!
If anyone is looking for them, we have put together throttle and cable kits in our web store here: www.BcShop.Barnstorm.US.