K100RS idles high

[lostbearings]

I bought a 89 K100RS last fall and spent the winter doing all the maintenance work. It had been sitting for 6 years in a barn and I was told that the old gas had been removed and flushed by the dealer. When I got it, and in the spring, it ran fine, idling at 1100 RPM. But it was difficult to start when cold.

So I ran the tank to as empty as I could, filled it up with new gas and added some fuel injector cleaner. Now after 30-40 miles of riding,it idles at 1700 RPM! The temperature gauge now races up toward overheating (when sitting at a stoplight).

The throttle cable has 1 mm slack and the throttle body valve is resting on it's stop. Why the high idle all of a sudden?

Any ideas?

Thanks

[roy]

Have you checked for vacuum leaks between the air box and intake. A leak will sometimes make an engine idle faster not sure if it would make run hotter though.

[breyfogle]

The throttle cable has 1 mm slack and the throttle body valve is resting on it's stop. Why the high idle all of a sudden?
Any ideas?

Is there any slack in the fast idle cable ?

[lostbearings]

Is there any slack in the fast idle cable ?

Fast idle cable?


I thought there was only a throttle cable and a choke cable. Is there another?

Jerry

[breyfogle]

The "choke cable" really just sets a faster idle by opening the butterflies a small amount. It is the cable at the rear of the TB assembly just in front of the TPS. There is no "choke" in the traditional sense on K bikes.

[PGlaves]

If the throttle plates are closing - that is they are not being held open by either cable - then the first step is to turn all 4 BRASS idle air screws in till they lightly seat and back out 1 turn. If that doesn't drop the idle you most likely have an air leak between the throttle bodies and the head.

[PGlaves]

One other possible cause is the TPS (switch) on the back of the throttle plate shaft on the #4 (rear) cylinder. If improperly adjusted it can hold the throttle slightly open.

[lostbearings]

One other possible cause is the TPS (switch) on the back of the throttle plate shaft on the #4 (rear) cylinder. If improperly adjusted it can hold the throttle slightly open.

I went looking for a obvious cracked rubber bit, and found all 3 vacuum plugs on the throttle bodies are cracked. Maybe they are the leak? I will replace them next week.

The TPS switch goes "click" after the trottle starts to move so I think it is adjusted correctly. I will check it with a meter next week also.

I am off to Boston to run in the marathon so the K100RS will have to wait until my return.

Thanks for the suggestions.

Jerry

[breyfogle]

The TPS switch goes "click" after the trottle starts to move so I think it is adjusted correctly. I will check it with a meter next week also.
Jerry

This past summer I had the same symptoms on my K75. After much trial and error, and help from this forum, I learned that the TPS has an internal stop in the closing direction *AND* a "click" in the opening direction. If the TPS is over rotated CW (looking fwd), its internal stop will hold the thottle plates open when the throttle cable is in the fully closed position. It will continue to "click" as the throttle plates are pulled open however. It's kinda obvious now but I have never seen it written anywhere that the TPS can be over rotated CW.

[lostbearings]

Well thanks for all the help. I found the problem and it was not anything anyone suggested. But your suggestions helped me find the problem by eliminating items.

Each air screw was out 1 1/2 turns so I turned them in to 3/4 turn. Minor change so I left it at 3/4.

Then I disconnected all cables and still the throttle assembly would not rest on the idle stop. Then I saw it.

Each throttle body has a throttle plate. Each plate is connected to the next with a lever which has an adjusting screw to sync them all together. I suspect the previous owner adjusted throttle body plate #4 so that it was closed, but ended up opening the other 3. This gave me the high idle. So what was happening was 3 plates were open a crack and 1 plate was closed. Once I adjusted it the same as all the others, it settled right down. Minor screw adjustment, no parts to replace.

I will need to do a proper syncing of the throttle bodies and adjust the valves. I will do this after a month or so of riding to loosen up this bike that was sitting for 6 years.

After doing all this I thought I would check that the over temp light works and that the fan works. Light OK, fan DEAD. Oh well, one problem at a time.

Jerry
81R100
89K100RS

[cjack]

Each throttle body has a throttle plate. Each plate is connected to the next with a lever which has an adjusting screw to sync them all together. I suspect the previous owner adjusted throttle body plate #4 so that it was closed, but ended up opening the other 3. This gave me the high idle. So what was happening was 3 plates were open a crack and 1 plate was closed. Once I adjusted it the same as all the others, it settled right down. Minor screw adjustment, no parts to replace.

I will need to do a proper syncing of the throttle bodies and adjust the valves. I will do this after a month or so of riding to loosen up this bike that was sitting for 6 years.

After doing all this I thought I would check that the over temp light works and that the fan works. Light OK, fan DEAD. Oh well, one problem at a time.

Jerry
81R100
89K100RS

These throttle bodies are synced at the factory. BMW always says that if someone turns the blue painted screws, the whole TB assembly needs to be replaced. I figure you can get them back where they belong close enough. You may have already. I would make sure the timing was correct before I adjusted anything else.
As far as the fan goes, I would fix that first.