It's the throttle sensor/actuator whatever they call it in the handlebar. It has gotten progressively stiffer and stickier over the years.
I finally got a chance to look into it and decided I'd tackle it. They're only $107 at the dealer, but I'm tired of throwing good money after bad, so I went for it.
I have to say that this is something the mechanically inept will not want to do. And I HIGHLY stress that in no way should you attempt it if you are not completely confident in your skills. I am, therefore I did. But if you get it wrong there is the chance of the throttle sticking and I won't be held liable for something you do wrong. I am willing to test and experiment and I have years of doing tedious electronic/mechanical work.
The problem is the material used inside the sensor and the design. It's a good enough design, and I haven't figured a better way, but the glass impregnated nylon, while being very tough can become abrasive/abraded by the very glass inside it, causing it to become resistive. And it really probably is the best material that can be used.
The mechanical (moving) part of the sensor is basically a twist shaft with a sliding, spring loaded cam riding over a fixed, matching cam at the end of the sensor body (towards the frame).
There is a "Heated Grips" wire attached to the shaft. It's the black one every body wonders what it's used for. Don't worry when you pull the shaft out, this wire will come out with it, unless it is hooked up to heated grips. Then, I don't know how it is disconnected, but if you do, then just disconnect it and pull it out with the shaft. There is a fairly large hole in the end of the sensor body (towards the frame) through which the wire, and I'm certain, contaminants will pass.
These parts are made of the glass impregnated nylon.
I was trying to spray lube on the end of the shaft where the spline is. This will never work as you can see from the pics. It is the shaft and the face of the cam at the other end that have to be lubed. GIN is best lubed with white grease or wax. I didn't have the white grease, so I used regular ol' Carnuba wax. I wanted a dry, long lasting lube anyway. Wax works exceptionally well in this application. Be warned that certain greases and silicone lubes can actually make the GIN stickier.
My result is pure smoothness. The throttle feels perfect now.
I began by drilling out the four dimples in the outer (metal) sensor body with a #33 drill bit and used 4 each 4-40 screws to go back with. I tapped the nylon collar to accept the screws, made sure the threads would not go through the collar and contact the shaft, and counter-sunk the place for the screws a little and smoothed the head of the screws so the sensor would go back into the handlebar. The screws ended up only having about a thread and a half left, which is no problem since they really don't clamp anything, they are just "replacing" the dimples. But if you do it right they can be tight. Three of mine were, I'm not worried about the fourth.....read on.....
I used 4-40 countersunk screws scavenged from my RC airplane bin. I haven't used any type of locking liquid (Locktite or epoxy) on the screws as I was afraid of it contacting the shaft, and they are captured by the inside of the handlebars since they are actually inside them. I will keep an eye on them and see if they need to be glued, but they really are held in place tight enough I believe.
After I drilled the dimples I pulled the mechanism out from the body of the sensor.
The body is where the electronics of the system are. The magnet is in the twist shaft. I believe the spring may actually be what causes the reluctance change now that I think about it. The spring is compressed by the cam as it slides along the shaft as you twist the throttle. The nylon cam, the spring and the shaft are the only three pieces that move.
For those who don't understand how this system works, when you twist the throttle that causes a cam to compress a spring on the shaft causing it to move inside a magnetic field thereby changing reluctance in a coil of fine wire, two coils in this case because it is a redundant system. This change is what the computer senses and is a very simple, robust and reliable system actually. I was not afraid to rough it up a bit because I figured there was a high likely-hood of breaking it anyway. I wanted to see just how tough the system is....after my ordeal, I'm happy to say you don't have to worry about being gentle with this unit.
The toughest part of doing this job is being patient and good with a dremel tool and small parts drilling. If you feel you are competent with such skills, then this really isn't too hard a job. It took me probably 4 hours to complete, and that's with it being a learning experience, and taking pictures. Now I have a system that when/if it starts sticking again, I can go back in and readily service it with no hassles. I could clean and service it in probably thirty minutes now.
Tools used were a hand drill, #33 drill bit, #43 drill bit, 4-40 tap, 100 degree countersink, dremel tool with sanding drum, x-acto knife, pliers, magnifying glass, alcohol (the cleaning type NOT installation fluid!!!) and Maguiars Carnuba wax.
Last edited by DC-3Mek; 10-21-2012 at 11:42 AM.