87 K100RS Missing Badly - K-Bikes.com - Excellence in Motion
 
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post #1 of 3 (permalink) Old Jan 18th, 2013, 2:15 pm Thread Starter
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Join Date: Jan 2013
Location: Walnut Creek, CA, USA
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87 K100RS Missing Badly

I have an 87 K100RS with almost 100k miles on it. The bike is missing very badly and my mechanic and I are both stumped. Here are some of the details. Any thoughts?

- Bike is hard to start when cold. When warm, it starts right up
- The miss happens when cold or warm
- There is a very audible clunk
- I replaced the L-Jet fuel injection control unit and we thought that fixed it, but no luck.
- For a few months now, shortly after start when I first ride, I would get a very bad hesitation when in first - so bad that when turning from a stop it almost dies.
- The bike will now slowly die shortly after start if I don't keep the throttle slightly open. This has gotten progressively worse over the past couple of weeks.

I am at a loss. Any help would be greatly appreciated.

I have a video of the problem is anyone if curious.

Thanks!
craigvega is offline  
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post #2 of 3 (permalink) Old Jan 23rd, 2013, 5:12 pm
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Sounds like what was happening to my until just recently.

It sounds like you might have a major vacuum leak or your throttle bodies are out of whack. Have you tried spraying starter fluid around the intake to see if the idle increases?
Have you tried to sync the throttle bodies before?
Also have the small screws set by bmw have their blue thread locker in place? The body has the adjustable screws that are larger and small ones that should not be messed with.

I'd start there. You can also briefly start the bike and check the exhaust manifold and make sure they are getting nice and hot. That way you can see that it is running on all cylinders. From there you can check injectors, plugs, coils...

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lukeman is offline  
post #3 of 3 (permalink) Old Jan 28th, 2013, 9:36 pm
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Location: York, PA, United States
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Crankcase breather hose

Quote:
Originally Posted by craigvega
I have an 87 K100RS with almost 100k miles on it. The bike is missing very badly andthe mechanic and I are both stumped. Here are some of the details. Any thoughts?


I am at a loss. Any help would be greatly appreciated.

I have a video of the problem is anyone if curious.

Thanks!
I have the 85. Easy way to check for vacuum leak is to start the mc and take off the oil cap.
There should be a noticeable difference in the roughness of the idle. No difference is a good indication of a vacuum leak.


First place I would look is the crankcase breather hose. This is a short s-shaped rubber hose that has a tendency to dry out and crack over time. I just did mine. This time I wrapped it in electrical tape for added support.

The hose can be accessed from the left side of the machine. Look at the engine just in front and above the coils. It is hard to replace w/o removing a bunch of stuff. I have done it but it is easy to tear doing it this way. I also believe the tube is asymmetrical. There is a right and a wrong way to put it on. I only discovered this by taking the mc apart to ease installation.

I can post a picture if you cant find the hose.

My K75 developed similar symptoms around 200k. I tried replacing the injector gaskets with no luck.. I didnt know about the breather hose at that time. Drove me crazy.
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