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?