I'm re-aquainting myself with the K again, and I tried something differrent. 

Ive ridden a few miles over the past days and it was going well with no issues, but today I had a problem. One thing is different - which may or may not be coincidence. I removed the Harmon chip I've been trying out and replaced it with the standard OE chip as I was curious to find out how the bike felt. 

The bike was running fine, then all of a sudden the engine cut, the two red lights appear on the instrument panel at the same time as the fan coming on. I popped the side panel off and jiggled the fuses, switched on the ignition - no fan - good to go.

It happened a couple of times after that, and a play with the fuses got me running again and heading towards home. On the last time it happened a couple of miles from home and no fuse fettling would get me going. Turn the key - fan going wild. I took each fuse out, inspected, cleaned (as best I could at the side of the road) and when the key was turned the fan was blasting out. No start. And then psyching myself up for the push home I tried again. Turned the key, no fan, it started and it was ok. Got me home no problem.

When I got back home I took each fuse out and gave them a good clean, and it now appears fine. I'll give it another trial run tomorrow.

I wonder if there's a link with me switching the chip in the Motronic box or if I just happened to coincidentally suffer from some electric gremlins?

Anyone come across the 'cut out - screaming fan - not starting' issue?

Did you clean the receptacle for the fuses???  A shot of Deoxit in there should help if that is the problem.  The fuse holder is in a rather vulnerable location if the bike is run frequently in bad weather.

It's also possible that your fuses are bad.  Several of the inmates here have experienced perished fuses that still had visibly good fusible links.

I would clean up the fuss holder and replace the fusses. You can always keep the old ones for spares.
Some years ago I had issues with a BMW car with the older style spade fusses where the fusible link bit was just an exposed bit of wire.
I had intermittent problems and had even tested the fuse that was the issue. About the forth time I pulled it and tested it it show as bad.
Since then I just pull them and change them when in doubt. If I had changed it the first time I would have saved a towing bill.

Would be interest in how the next ride goes after a cleaning and replacement?

..as an aside, Ive also noticed that ALL the fuses in the box are 15A.

That's not right is it? (1990 16v if that makes a difference)

1992 K100rs owners handbook say 15amp for all seven of the normally used fuss. For 8,9 and 10 it depends what you have on them

Thanks gorio, I'll dig out my handbook to make sure 

Just found it.

All 7 fuses are 15A.

I replaced all my fuses will ones that have a built in LED light the illuminates when the fuse blows. At the same time I also purchased some circuit breakers that replace the fuse. They have a tiny button that resets the breaker once tripped, they're a little taller than the standard fuse and I don't think they'll fit under clear cover. However they're great for diagnostics and replacing blown fuses on the side of the road.
Regards Martin.

MartinW wrote:I replaced all my fuses will ones that have a built in LED light the illuminates when the fuse blows. At the same time I also purchased some circuit breakers that replace the fuse. They have a tiny button that resets the breaker once tripped, they're a little taller than the standard fuse and I don't think they'll fit under clear cover. However they're great for diagnostics and replacing blown fuses on the side of the road.
Regards Martin.

Great idea   

You don't happen to have a picture do you Martin?

After thoroughly cleaning the fuses yesterday, I did a good 60 mile run out today, some of it in biblical downpours. Happy to report there were no cutting out issues, so it seems that it was the fuses after all. New fuses on the way.

Also glad that there was no link between the bike cutting out and me swapping out the chip.

Glad to hear it was a relatively easy fix once you got back home. You have added one more item to maintenance list as spring riding starts up here on Vancouver Island.

Sorry about the rain.

gorio wrote:Sorry about the rain.

Rain isn't a problem with the excellent RS fairing 

Blade circuit breakers and blade fuses with LED indicator can be bought at any good electronic store or online through Aliexpress.
Regards Martin.

Cheers Martin,

Great job. I can see that the circuit breakers would be too tight a fit though.

I don't have the circuit breaker ones fitted but I carry them as spares. They are there to be used for roadside diagnostics if a short develops. It beats replacing fuses if a fault does develop. However you could run them if you run without the cover or join two covers together to make a taller cover.
Regards Martin.

Sounds like the Motronic may have gone in to a fan test mode with your chip swap or other related Motronic gremlin.
If there was a Motronic fault generated you probably cleared all by removing fuse #5 a number of times.
Disconnecting battery or Motronic connector will also clear/erase fault code.

from diagnostic manual
The Motronic System has the capability of monitoring its operation. When a malfunction occurs, the Motronic Control Unit (MCU) detects it and stores the information about the malfunction in a portion of the control unit known as the fault memory. The information in the fault memory is in the form of a numeric code. These codes correspond to an actual circuit or component that is found to be defective on the system.

If a fault is detected, the MCU will provide a substitute value for the faulted signal. This allows the rider to continue riding the motorcycle, even with a fault in the system, to obtain service.

The only input signal the MCU does not provide a substitute value for is the engine speed and reference signals produced by the hall sensor. The MCU will set a fault code but can not function without this signal

Two Motronic Systems are used: M2.1 with CO potentiometer (without catalytic converter) and M2.2 with O2 sensor (with catalytic convertor). The fault codes other than the CO potentiometer (M2.1) and O2 sensor (M2.2) codes are the same.

The Motronic System relies on signals from the idle CO potentiometer and the throttle position potentiometer for correct mixture throughout the RPM range.

Service Bulletin  Fuel Supply & Adjustments  September 1991   13 023 91 (2475)

http://www.k11og.org/forum/viewtopic.php?t=2110&start=0&postdays=0&postorder=asc&highlight=

http://www.largiader.com/articles/motronic.html

Great info volador, thanks for posting