Oilhead Tech Pages


The Case of the Sticking Fast Idle Cable
or
How to Replace Throttle Cables and Service the Cable Junction Block on a Late Model Oilhead

   Bryan Lally


Bikes effected:

These instructions are for an R1100RS with the cable junction block (crank wheel) throttle cable. It should be a very similar operation on any of the oilheads except for the differences in fairings and trim parts. These instructions do not apply to bikes with the crossover cable throttle arrangement.

Why did I do this?

The fast idle cable on my oilhead (at 3400 miles) started to "stick." When the fast idle lever was moved from the normal position to the detent or start position, the cable worked normally. But when the lever was returned to the normal running position, the cable would go very slack and the throttle butterflies would not return to the idle stops. Putting tension on the throttle cable would cause the fast idle cable to snap back to its normal state (and the butterflies would close).

After some thought and considerable pulling and wiggling of cables, I decided I needed to take a good look at the junction block assembly.

Short Story

The fast idle cable pulls on a small ramp, which pushes on a flat on the crank wheel, turning the wheel and opening the throttle butterflies by way of two short cables. The ramp acts like a wedge between the flat on the wheel and the slot that the ramp slides in. There is a return spring for the fast idle ramp and cable located at the junction block assembly. The ramp would not release from its wedged position; it was being held in place by the tension supplied by the throttle butterfly return springs through the short cables. As soon as the throttle handgrip was turned, the ramp was released from contact with the crank wheel and returned to its rest position by the fast idle cable return spring. The junction block assembly was put together completely dry, with plastic sliding on plastic. A small amount of grease was used to lubricate the ramp and the slot that it rides in; this elminated the clamping effect on the ramp and fixed the problem. In my opinion, this should not have been assembled dry.

Replacing Throttle Cables on Junction Block (new style) Oilheads

Remove the seats.

Remove left and right fairing pieces.

Remove the air snorkel that feeds air to the air cleaner.

Remove the fuel injector covers.

Unplug the wires that trigger the fuel injectors at the injectors, or else they will be in the way.

Remove the two screws that connect the upper fairing to the front of the gas tank, and the two screws that connect the fairing insert pieces to the front of the gas tank.

Remove the throttle cable from the twist grip (remove the small cover that the cable goes into).

Remove the fast idle cable from the fast idle lever (pry off the "choke" cover, and unscrew the large screw).

Remove the short throttle cables from the pulleys on the throttle bodies and unscrew the adjusters from the throttle bodies.

Unplug the gas tank connector from the wiring harness, and remove the connector from the tab on the frame.

Snip the cable ties that hold the fast idle cable and the throttle cable - there are several.

Pull the right hand short throttle cable so it comes out _under_ the crankcase ventilation hose. Remember when you put things back together that it goes _over_ the hose.

Pull the throttle cable out also under the crankcase ventilation hose.

Note where the left side cables exit the bike.

Now remove the cable junction block. This is the small plastic piece that the cables disappear in to. Removal is done from the right side of the bike. There is a clip on the underside of the block, which must be held down while the block is pulled out. I had to slightly bend the tab that holds the fuel tank electrical connector up so that the cable junction block would clear it on the way out. Then I was able to wiggle the cable junction block out underneath the crankcase ventilation hose.

Note: the manual says to remove the engine block end of the crankcase ventilation hose. I was able to leave this attached. The hose clamps are the use once kind that require special pliers to replace, and there is very little room to use a screw type hose clamp. Don't remove this hose unless you really have to. If you have a tip here, I'd like to hear it.

With the cable junction block out, it should be clear how to replace the throttle and fast idle cables.

The crank wheel is held in place with an E clip; remove the clip and you can take the crank wheel out. Now you can clearly see the sliding ramp that needs lubrication. Any kind of grease should work fine for this application.

Assembly is the reverse of disassembly (I always enjoy reading that). Don't forget the cable ties. You will also have to do a complete throttle body sync when you've got it all assembled. You should not have to readjust the TPS.

I don't think that replacing your throttle cables is something you're going to want to do on the side of the highway, in the dark, in the rain.


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R-Tech pages maintained by: John Petty for the original author(s) and the Internet BMW Riders
Last Update: 09 September 2010