1
early K100RS hard start, dies at stop signs Sat Aug 24, 2019 8:43 pm
mibh
![mibh](https://i.servimg.com/u/f41/11/71/56/74/avatar10.jpg)
active member
![active member active member](https://i.servimg.com/u/f80/11/71/56/74/bmw-1s10.gif)
#0018458 (K100RS, EUR, 05/1984, code 0503) has taught me a lot about air leaks in the intake, and how beastly a beauty can be. it's in denmark, and i'll be visiting it in mid september, and i've set aside a day of repair before i ride down into germany. the previous owner did a wonderful job on the paint and powder coating but appears to have pulled and reinserted the engine and drive train without taking it apart. so, we've gone through it extensively, including all new rubber in the intake, all new vacuum hoses, new plugs and wires, spline lube, all fluids. this bike has taken me across sweden into estonia and down through latvia and lithuania and then back through sweden; it's also made the reverse loop but also including finland. it's pretty solid. you can see from the picture below that i put LT bars on it. you can't see from the picture that the damned mirrors keep falling off and so one fix i'll be doing shortly is to put stock K100 (short) mirrors on it, brush guards with integrated turn signals, and then i'll remove the mirror/signal ears and take it to a body shop for fill and paint. (this is a change i've enjoyed on the similar bike i keep at home in california.)
anyway there are two tuning/running issues that i'd like to diagnose and fix:
1. takes ten to 20 minutes to start up, even in shirt-sleeve weather. i am always the last biker off the ferry because i have to start it a dozen times and feather the throttle until it's hot enough to start the fan running -- otherwise it dies as soon as i apply power.
2. dies when returning to idle after running at speed, like when coasting to a stop sign. even if i downshift and apply engine braking in every gear on the way down, it will die when i clutch for the stop. i usually then pop the clutch to make it start again, and feather the throttle until i can start up again.
by now i have replaced the coolant temperature sensor, cleaned and tested every harness connection, cleaned and tested the idle switch, cleaned and tested the enrichener ("choke") mechanism, since this is a 280Z-era bosch jetronic system and i know its weaknesses well. also replaced the vapor recovery hose, and every bit of rubber and plastic in the intake system. and of course i've acquired the necessary spare AFM and ECU, and have cleaned those connectors as well. i used to have worse problems with this bike! but i still have two.
astonishingly, i have not checked the ignition timing, hall sensors, or fuel pressure. so, those are next.
however, if my symptoms sound familiar, and you have additional advice, you will find me an avid listener.
![early K100RS hard start, dies at stop signs Img_2020](https://i.servimg.com/u/f93/20/10/34/03/img_2020.jpg)
anyway there are two tuning/running issues that i'd like to diagnose and fix:
1. takes ten to 20 minutes to start up, even in shirt-sleeve weather. i am always the last biker off the ferry because i have to start it a dozen times and feather the throttle until it's hot enough to start the fan running -- otherwise it dies as soon as i apply power.
2. dies when returning to idle after running at speed, like when coasting to a stop sign. even if i downshift and apply engine braking in every gear on the way down, it will die when i clutch for the stop. i usually then pop the clutch to make it start again, and feather the throttle until i can start up again.
by now i have replaced the coolant temperature sensor, cleaned and tested every harness connection, cleaned and tested the idle switch, cleaned and tested the enrichener ("choke") mechanism, since this is a 280Z-era bosch jetronic system and i know its weaknesses well. also replaced the vapor recovery hose, and every bit of rubber and plastic in the intake system. and of course i've acquired the necessary spare AFM and ECU, and have cleaned those connectors as well. i used to have worse problems with this bike! but i still have two.
astonishingly, i have not checked the ignition timing, hall sensors, or fuel pressure. so, those are next.
however, if my symptoms sound familiar, and you have additional advice, you will find me an avid listener.
![early K100RS hard start, dies at stop signs Img_2020](https://i.servimg.com/u/f93/20/10/34/03/img_2020.jpg)