I’m having a problem with my 1987 BMW K100 RS. I got the bike used, but in very good shape and rode it for two years without any major problem. At the end of the season in 2004 while I was riding the bike to its winter home the problem started. I’m going down the interstate at about 80 mph, the bike sputters and stalls, comes back on, and then completely shuts off. I’m now coasting with the stalled engine dropping my speed rather fast. After I made it to the shoulder and stopped I made sure the bike was in neutral and tried to start it. The fuel pump came on and the starter kicked in, but the engine would not start. Long story short, after about 20 minutes the engine decided to turn over and run for about 5 minutes down the road only to occur again.
This spring (2005) I took the bike to the BMW dealer in Ledgewood, NJ to try and find the problem. I left it with BMW in April, and got it back in August; when the dealership went out of business. They had been telling me that it is an electrical problem but were unable to narrow it down. After a bit of testing on my part, for example; ride until it dies, then sit and wait for 30 minutes and try and ride again. I have found that it will run for about 25-35 minutes, seeming irrelevant of miles, before it dies. When you restart it, it runs for a much shorter time maybe 5-10 minutes before stalling.
I know the cooling fan on the bike is not working, but I have also tested that and the fan never tries to turn on and it dies anyway. I also know it is not the major computer components, as these were swapped out with another working bike while it was at BMW and the same problem still occurred.
Does anyone have any idea what could be wrong? I love the bike, and it runs beautifully when it runs at all.

Mark Vergalito, October 2005

As this is an old post I assume the fault has been fixed, this may be of help to others. I have had these exact issues on my K75. I traced it to water in the fuel. If this happens check if the fuel looks cloudy, the pump mixes the water and it takes about twenty minutes to settle out again, allowing the bike to start again until it mixes and repeats the problem. Also check the starter motor for brush failure as this can cause problems.

Rob, September 2011

Make sure you have fuel tank vent is not pluged. Check and make sure you have spark to the plugs, when it stops. Also make sure the fuel pump is not getting hot and stops, check pressur.

jack, October 2009

BMW here told me that they had a simlar problem some time ago. It was the brushes in the stater motor shorting to earth and operating the load shed relay.

rod cmcmahon, September 2009

Hi did you solve your problem at the end? I own a lovable k100rs 16v whit same symptoms. Unluckly, now, after few restarts and stops and having replaced a new battery, doesn't work anymore... so sigh!

Gilberto, July 2009

Ok, this is what solved the problem:

the Halls Sensor or better known as the crank position sensor. This part reacts to the heat from the engine causing it to malfunction and cut the engine. After the engine cools it resets itself and functions again.

Good luck!!

Mark Vergalito, August 2008

I had similar problems on myK100 RT and the reason was fuel heating causing gas pockets in the lines , The later models after 1986 had a new pump which kept higher pressure and a heat insulation under the tank. I used to open the tank filler and allow out the fumes . The only trouble with your is that it did it in winter whilst mine was summer.

G. Dawes, June 2008

My K100RS did this last summer. The fault was traced to the battery which was old but holding enough charge to start the bike.
Changing the battery cured the fault.

Ted Andrews, March 2008

My K100RS did this last summer. The fault was traced to the battery which was old but holding enough charge to start the bike.
Changing the battery cured the fault.

Ted Andrews, March 2008

archie is nearer the problem it can also be the cdi unit or ignition pulser coils failing its almost certainley electrical as heat is the reason its breaking down hence why it does it when its warm i had the same problem with a honda nsr 125 once and it was the primary ignition coil on the stator plate which would seperate slighlty when it was hot and was fine when it was cold ok, adam

adam, December 2005

It sounds as if ,presuposing the fuel pump is pumping that the component failure will be one that is being subjected to heat and then fails...which I would assume to be a CPS sensor...you will have to check there is a spark when it fails..and also that Fuse No 8 is intact and connected, as this runs Fuel Pump relay....

lobofuego, December 2005

Although I am not very familiar with the K100 engine management/ ignition set up. I would say these are classic symptoms of ignition coil breakdown. I suggest you start by replacing all ignition coils.

Archie, November 2005