Hi,

Last Sunday, about half an hour into a ride my 1989 K100RS SE (8v head and 1.5 ABS) had a hissy fit.  It started misfiring as if from fuel starvation and then almost immediately the ABS and brake light warnings started flashing.  The misfiring passed and after a short time was running cleanly with full performance available.  I had refuelled shortly beforehand and had a full tank.

It briefly went through a similar misfire routine two weeks ago after running for about an hour and then cleared itself. First off I am going to replace the new fuel filter just in case and treat the fuel in case there is water contamination. 

The ABS is a bit more of a concern and I need to understand if the misfire AND ABS warning are coincidental or bad luck.  The battery is off to be thoroughly tested tomorrow.  It would sort of be nice if the problems are simply related to the battery.  Feels unlikely though as the problems both times were after the bike had been running for some time.
I have read all the good advice from our friend in Japan and I am getting ready to do more checks this weekend.  I want to isolate the ABS brain so that I can still safely ride the bike without ABS.  Now come the stupid questions but I work on the basis that the most stupid question is the one you don't ask...
1. How do you get the ABS brain out?  I assume the two little screws on the top edge of the tail piece will release the two brackets to drop the module out?  Does the connector simply pull out or are there hidden pins to remove/release first?
2. I cannot find the diagnostic tool input plug which is needed to connect the mid pin to earth to clear the brain memory. (See I have been reading the advice!)  There is no sign of anything under the seat or near the battery.  I have an idea what I am looking for from the various manuals, but I cannot see anything resembling three cables routing into a three pin plug without an apparent further connection.  Any clues or where to track the cables from?

Regards
Nigel

Nigel,

Can't say for sure, but fuel starvation and coincident flashing of ABS and Brake warning light suggests to me that the root of the problem is electrical (possibly something in the ignition circuit) - you are checking your battery (good place to start) and its worth checking your fuses too (with a test meter)? Are you losing anything else at the same time?

It sounds like you are having a power loss that is both cutting power to the fuel pump and turning off the ABS. When the power comes back, the ABS and brake light will flash like they do when the ignition is first turned on, but the brain may have thrown up a fault code and may not reset itself.

ABS module removal is easy - release the two screws attaching the mounting cradle to the ducktail.


Removal of the plug, needs you to release the shiny straw coloured clip (I think it is press to release, can be quite stiff)
 

The ABS test connector is on the right hand side of the bike, often tucked up under the top of the frame.


Good luck with your fault finding.

Thanks Paul!  Excellent pictures. I will post later how the battery test went.
Regards
Nigel

Battery test reported a satisfactory result.  Two cells were short of fluid (oops! Too used to gel batteries) which was sorted.

I have now found the diagnostic point thanks to Paul's image.

Tomorrow I will refit the battery, clear the ABS brain, check for water contamination in the fuel, change the fuel filter, put some injector cleaner in the fuel, contact cleaner on the ABS connections and check the plugs. Next, crack open a cold beer to either celebrate or consider life without ABS...

Regards!
Nigel

Hope all goes well. I wouldn't be too hasty to remove the ABS permanently - it is a useful safety feature and may not the the cause of your problems, just an innocent victim of low voltage.

Came across this recent post, which may give you some ideas too...
https://www.k100-forum.com/t9851-battery-replacement#116922

Looks like Point Seven Five has had a similar power drop while riding and cleaning up the ignition switch seems to have cured him (very clear step by step instruction attached)....might be worth dropping him a PM for more details of his symptoms etc.

Phew! Reset ABS and fault light has extinguished! New fuel filter in despite fuel and tank looking clean from contamination. Wurth injector cleaner added. It may be coincidental but the ABS connector may well have just been a loose fit as the clip was not engaged and the connector fell out as I removed the module. Connectors cleaned and securely replaced.

Flying Brick will hopefully be flying tomorrow! Many thanks Born Again Eccentric and to Mike Delacor (if you are reading) for all your help and encouragement.
Regards
Nigel

Nigel - Good result - enjoy the ride tomorrow.

Hi,
A month on and I thought I would post an update.

On Wednesday the Brick was running really well in the morning when half way through a 70mile journey on a motorway the misfire/fuel starvation kicked in again. within 5 minutes of travel it had cleared. Plenty of fuel on board and it ran perfectly for the next 100 miles including slow very hot running in traffic. There had been another episode like this 2 weeks earlier, the issue seems to occur every 500 miles or 3rd tank of fuel. Odd. I am going to replace the plugs, leads and plug caps and gradually tick off possibilities but I wonder if it is poor fuel, anyone else finding the 1980's fuel injection struggling with modern unleaded?

Then to round off the day the ABS light came on on the run into home. Today I reset the light, no effect, took the ABS brain out and noticed again that the connector appeared loose. I very firmly connected up again and put a Velcro strap around the unit and connector to make sure. Refitted, reset the light and no more red light on!

The Brick is now well into what it was bought for, doing long runs taking me to work assignments, this week it was over 500 miles in three days across the south of England. Good fun!

Regards,
Nigel

I would as BAE said be looking at the ignition switch. I had strikingly similar problems with the K100 and the R80RT both have the same switch and it was the problem. Both times it needed replacing because it was well worn and had no tension on the contacts. Both had over 250k on them and couldnt be fixed but if yours is considerably lower in miles then give the clean a go it will probably work.

Thanks! The bike is only 58k miles so worth checking the switch. 
Regards
Nigel