One think I love about the brick is the rock solid idle. It's cool to hear that thing puttering away. So I was a little bothered by the fact that my K would not want to idle after a long drive. I recently put 500 miles on on a drive to Alpine Lake CA and the temp ranged from 101F to 37F. In the heat, the bike would stall at lights if I didn't give it throttle. When the temp dropped, it seemed to idle fine.

What made matters worse was after I returned home, I filled up with fuel (91 Chevron, I think) and for the next 150 miles, the bike ran like crap. Would not idle at all, and would sputter and miss at low RPM. Drop in power, too.

Felt like a defective coil.

Yesterday, I filled it up with Chevron 91 (from a different station) and it seems to run better. Well at least I can drive it without "nursing" the throttle at lights to keep it running.

I wonder if I got a batch of bad gas?

I wonder if my heat-soak idle problem is still there?

I'm going on a 500 mile ride next Sunday. I guess I'll find out.

Anybody carry a spare hall effect sensor, coil, etc in their tail cone for such problems?

Scottie

Hi Scottie,

You have to wonder how accurate these octane ratings are and I bet if measured from different stations they would all be different. Recommended octane rating for mine is 98 so that's what I use although not that easy to find plus a lead additive which is also supposedly an octane booster.

Even my lawnmower will not run smoothly on the 91 we have here so it and my wife's car run on 95 even though they are supposedly capable of running on lower.

Your problem certainly seems fuel related so I guess your ride on Sunday will tell you one way or the other.

Regards,

Phil

Hi Scottie,
Why not fill up with higher octane 95 or 98 to see what the effect is?
It cannot harm the bike to try that.
Regards,
K-BIKE

Hi Scottie,
Have you tried a plug swap sometimes a bad plug can cause the symptoms you describe. Known good spark plugs is worth doing, when did you last change the plugs?
Regards,
K-BIKE

3 weeks ago, my K100 got exactly the same problem as the one that you described.
I was also thinking about ignition, bad gas or plugged fuel filter, but found a very different problem....

Let me explain:
I went for a ride and the bike was running fine. I stopped for 5 minutes at a store and when I restarted the bike, it wouldn't idle.
The bike was running great as soon as I throttled over 2000rpm. I went back home and stored the bike in the shed for the night.
Next morning, I decided to troubleshoot the problem.
First, I started the bike, and surprise, the idle was perfect. I let the bike warmed up and then it started to crap up.
I swapped the spark plugs, restarted but it was still not idling.
I started to check the electric connections, spark plug wires....... Then when trying to start again the battery went dead!
The battery is only a year old and always on battery tender during the winter.
(my next step would have been to check the water temperature sensor)

I took the battery of the K75 installed it on the K100, started the bike and could not replicate the problem. After charging the original battery for only 5 minutes, I tried it and it was working again.
I then checked the alternator on the K100 and everything looked good. What I found, is that the alternator doesn't produce power if the engine is running under 1200rpm.
The bike idle between 850 to 1000rpm and relies only on the battery to provide power to all the electronic and lighting system.

My original battery has certainly a bad cell intermittently shorting out and the voltage gets too low to run everything. This may occurs when the engine is running and the vibration of the engine shakes the cells of the battery. Could it be a loose cell ?????
Why the problem showed up only when the bike was warm is a mystery.
Since swapping the battery I put about 700kms on the bike and did not experienced anymore idling problems.

Let us know we you find on your bike.

Bert

Problem seems to be solved. I did swap plugs and that seems to have solved my problem. I may have had bad gas too?

I will also check the battery electrolyte levels (it's a BMW battery) not sure of its age. It was on the bike when I bought it.

Update: I thought would update this topic. The problem was not my plugs or wires, or hall sensor. The problem was defective coils. I have never had a defective coil on a BMW before, so I was surprised. Both coils were bad. Replaced both coils with parts from a parts bike, and my bike runs like new.

Hi Scottie,
Good news, now as a bit of data for the test schedule when the next person has the same problem, can I suggest you post the results here of the coil tests so this thread provides an answer for the future if someone follows this thread.
Regards,
K-BIKE

Yeah, good idea. Actually I had started two posts because I wasn't sure if I had an electrical problem or an engine problem.

The other post has the solution and coil measurements.

http://k100rt.aforumfree.com/engine-and-transmission-f10/poor-idling-and-low-rpm-power-returns-t406.htm

I just found my spare coil and measured it. I get 12.55 kΩ between 4a and 4b, and 2.6 Ω on the primary (between 1 and 15)