How to fix a Throttlemeister so that it won't self-lock

Problems with the Throttlemeister creeping toward the locked position and locking on its own are reported from a variety of unrelated persons and sources. At the same time, many others have reported that they have used the Throttlemeister for years without ever once experiencing this problem. Occasionally someone who has never observed the problem has expressed the strong opinion that it is caused by incorrect installation or adjustment, which of course is greatly appreciated by the people that have the problem.

My personal observation is that each time I remove and then reinstall the gizmo, there will be a good chance that I will have this problem until the next time I remove and reinstall it, at which point I will still have a good chance of having the problem, but also some chance that it will go away. I have long thought that the reason that this happens is simply that the outer part that rotates is not balanced, and that the random placement of the heavy side of that outer part determines whether or not it will have a tendency to self-lock. Lacking the requisite "round tuit", I had not attempted to disassemble the gizmo until a few days ago. This is the sort of thing that I typically tackle late one night when I am unable to fall off to sleep, so a few days ago at around 1 AM, I walked out to the garage, took the gizmo off the bike, and took it apart.

The picture above shows a grip that can be used to take it apart. The long screw, the insert that keys to the handlebar insert, and the spacers fall out when it is taken off the bike, and there will be a hollow space, where the out-of-work Hollywood actor that I hired for this reenactment, has inserted his left forefinger. The stainless steel inner sleeve that his forefinger is pressing against will easily slide longitudinally over a short distance. When it is pulled out that short distance that it moves easily, you can then unscrew the inner cylinder along with the bronze part, from the outer part, using your forefinger to exert pressure as needed, and squeezing between your thumb and forefinger if needed, until the inner cylinder and the bronze part are separated from the outer part.

Once the inner cylinder and the bronze part are separated from the outer part, the bronze part will slide off and away from the inner cylinder.

The picture above shows the main components (and one of my favorite pocket knifes). The inner cylinder is in the foreground. It is turned around backwards relative to the other two parts: the end that is facing the camera goes toward the closed end of the outer part that is on the left. The reason that I turned it around this away is so that you can see the channel that is machined into the end, running roughly 150 degrees around the circumference of the cylinder. Note the little bump that is machined into the inner surface of the outer part, at about the 7 o'clock position. When the inner cylinder is pushed fully into the outer part, the little bump engages in this channel, which limits the distance that the outer part can be rotated to 135 degrees.

The inner cylinder has what appears to be a long hump. This is actually a pin that sits in a groove, and the groove that you can see in the bronze part behind it, slides over that pin, thus preventing these two parts from rotating relative to each other. The special spacer that goes at the head of the long screw presses against the inner cylinder and prevents it from turning. Since the inner cylinder cannot turn, the bronze part is likewise prevented from turning by that long pin. The special spacer at the head of the long bolt also holds the outer part from pulling out, but it is machined so that it will do this without applying any pressure that would inhibit the rotation of the outer part.

The bronze part is threaded on the outside, and the inner wall of the outer part is similarly threaded. Because the outer part and the bronze part are threaded to each other, when the outer part is rotated, the bronze part, which cannot rotate, slides back and forth a short distance equal to the thread pitch multiplied by 135/360.

The little bump inside of the outer part is the reason that the outer part has a heavy side and is the reason that the gizmo will self-lock if it is installed with the heavy side facing the rear of the motorcycle. Given the minimal internal friction, and given the constant vibration, if it is installed with the heavy side toward the rear, the only uncertainty is how long it will typically take for the gizmo to self-lock. I am a little puzzled as to why Marker Machine does not acknowledge this. In the FAQ on their Web site, they say, "It will not Engage or Disengage automatically." I find it odd that a company that has created such a high quality product would be willing to compromise their credibility by making a claim that many people know from first hand experience is not true. I would suggest to them that a better course of action would be to machine a small dimple into the outer surface on the heavy side and state in the instructions that it should be installed with that dimple toward the front to reduce the tendency to self-lock. Perhaps I can send them this URL and they will agree that this is the appropriate course of action, and perhaps they will show their appreciation to me by sending me a free Throttlemeister for my Yamaha FJR1300!

What you need to do is mark the heavy side of the outer part, ideally in the red groove that runs around its outer circumference, so that your mark will not rub off when you reassemble it and reinstall it on your bike.

In the picture above, the out-of-work Hollywood actor that I hired, is re-enacting me marking the heavy side of the outer part. I used "liquid paper", and put the mark in the groove so that it would not wear off when I reassembled the gizmo and reinstalled it on the bike.

The picture above shows the first step in the reassembly. The bronze part is slipped over the inner cylinder.

Reassembly is a little bit tricky. In order to thread the bronze part into the outer part as far as it is supposed to go, you have to keep the inner cylinder pulled away from the end so that the bump will not hit the non-channeled part of the end of the inner cylinder.

Correct assembly has to be checked with the inner cylinder pushed in so that the bump is engaged in the channel, and with the gizmo rotated to the fully unlocked position. Each time that the two parts are mutually rotated a full turn, the bump and the channel will line up as required and it will be possible to push the inner cylinder in so that the bump engages the channel. It is actually possible to screw it in too far so that the bronze part will be recessed slightly into the outer part in the fully unlocked position. This is not good, because then when it is turned to the locked position, the bronze part will not protrude far enough to grip the throttle flange. If this happens, you need to turn it out one full turn so that the bronze part protrudes slightly in the unlocked position.

Here comes the surprising part. If you examine the threads on the bronze part carefully, you will see that it actually has two threads running alongside each other. If you run your thumbnail over the threads and count the thread edges as you go, the even numbered ones belong to one helical thread, and the odd numbered ones belong to a separate helical thread. Makes you wonder if Watson and Crick invented the gizmo, doesn't it?

When I was in college, a friend of mine had a Monty Python record where each side had two grooves that ran beside each other the full distance from the outer circumference to the inner circumference of the record. Depending on where the spinning record happened to be when you dropped the needle down on the record, you heard one or the other of the two separate tracks that were recorded on each side of the record. In order to hear the other track on that same side of the record, you had to pick up the arm and drop it down on the spinning record again, and you had a 50/50 chance of catching the other track.

There are two possible ways for the threads to engage, and when you get the threads started, you will have randomly selected one of those two ways. The other way would have been selected if you had started the threads with one of two parts rotated 180 degrees relative to where you did start the threads.

The specific way that you have selected will determine how far the bronze part protrudes from the outer part. This is not continuously adjustable, because the channel and the bump engage once each full rotation. One of the two ways will result in the bronze part protruding further than the other way, with the difference being exactly one-half of the thread pitch. When it was originally assembled, one of those two ways was selected, and if you select the other way now, then you will have to readjust the gizmo with different shimming when you install it. If you still have all the original shims then this is not a problem. If you no longer have those shims, you may find that you need to take it apart again and play with it until you have selected the other way for the threads to engage. If so, if you pay close attention and feel when the threads separate, you can then continue to turn an additional 270 degrees in that same direction before starting to screw it back together. If you do that carefully, with a little practice you can get it correct on the second attempt every time (almost).

The picture above shows the gizmo reassembled and rotated to the unlocked position, with the bronze part protruding .5 mm, which is the shortest protrusion that is possible without the bronze part being recessed in the unlocked position. In my case, it was originally installed the other way, and the distance that the bronze part protruded was greater than .5 mm by one-half of the thread pitch. I had to re-shim it, but this was not a problem and turned out to be desirable, because I discovered that when assembled this way, it actually operated a little better. It now has less drag in the unlocked position, a more positive grip of the throttle in the locked position, and it is not as sensitive to exact shimming as it was before. Perhaps there is some play in the threads when the other way for the threads to engage is selected.

The picture above shows the gizmo re-installed. The heavy side of the outer rotating part is now toward the front when it is in the unlocked position. As you tighten the long screw, tighten it to just to where you can still rotate the whole gizmo (the inner cylinder) with slight resistance. Rotate the whole gizmo in the unlocking direction. Rotate it until your mark is almost to the horizontal position as shown, but not quite that far, because as you tighten it down to where the inner cylinder cannot turn, the inner cylinder and the whole thing will turn a little further. After 2-3 attempts, you will have a feel for just how much further it is going to turn when you do the final tightening. Then you will be able to position it so that after the final tightening is done, the heavy point will be located at the furthest forward point, and it will then have a natural tendency to stay in that position.

Even though it took me a few hours to take these pictures and write this up, the time that it took me to do the fix was only about 15 minutes. If your Throttlemeister exhibits any tendency to lock on its own, then I encourage you to do as I have done, and in all likelihood, this will fully correct the problem, as it did for me.

Tom Barber

Copyright © 2003, by H. Marc Lewis and Tom Barber.
All rights reserved.