87 K100RS Missing Badly - K-Bikes.com - Excellence in Motion
 
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post #1 of 5 (permalink) Old Jan 17th, 2013, 8:10 pm Thread Starter
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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!
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post #2 of 5 (permalink) Old Apr 2nd, 2013, 9:11 am
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Location: Lake Forest, Il, USA
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Is this still an active problem?

'Sorry I didn't see this until now.

Solving problems via internet is hard, but there are several known problem areas with these early K Bikes as they enter middle age.

Fuel - Have you checked the fuel filter and in tank hoses? They are usually shot if original.
Undertank connector for fuel pump and fuel light. Check this - the female connector sleeves are often weakened and will occasionally lose connection, causing the engine miss.
External z hose - if leaking causes really poor performance and is due for replacement.

Let us know.

"What follows is based on actual occurrences. Although much has been changed for rhetorical purposes, it must be regarded in its essence as fact. However, it should in no way be associated with that great body of factual information relating to orthodox Zen Buddhist practice. It's not very factual on motorcycles, either."

Robert Persig - Zen and the Art of Motorcycle Maintenance


1985 K100RS (Sold)
2000 323i (Sold)
2003 1150GS (Sold)
2009 528Xi
2004 K1200GT
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post #3 of 5 (permalink) Old Apr 4th, 2013, 9:39 am Thread Starter
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Thanks. I recently had the fuel filter replaced as part of a service, but I don't know if they thoroughly checked the in tank hoses. I will check those this weekend.

I recently replaced the crankcase z breather hose but saw marginal improvement. Funny thing is that I now have intermittent speedo issues. I think I may have knocked something loose when I replaced the z hose. Do you have any recommendations about the speedo issue?

Thanks!

Craig
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post #4 of 5 (permalink) Old Apr 4th, 2013, 11:12 am
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You may have multiple small problems

Bike is hard to start when cold. When warm, it starts right up
Early K Bikes tend to be cranky when cold - but you live in the Bay Area, for pete's sake. It's not cold there.

The bike is missing very badly and my mechanic and I are both stumped.
Check that connector under the tank. See if you can simulate the missing problem by jiggling it. If so, there are multiple threads on how to solve this.

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.

This really does sound like a fuel problem - I'd remove the fuel pump from the tank and test it with a 12 volt signal and see if it's working properly - do this when you are replacng the intank fuel hoses. Very often the fuel pump damper is falling apart and dissolving - pieces of this can damage the fuel pump.

There is a very audible clunk
I haven't a clue based on this, I'd have to hear and localize the sound.

Keep us posted.

If you want to send me the video, it might help.

[email protected]

"What follows is based on actual occurrences. Although much has been changed for rhetorical purposes, it must be regarded in its essence as fact. However, it should in no way be associated with that great body of factual information relating to orthodox Zen Buddhist practice. It's not very factual on motorcycles, either."

Robert Persig - Zen and the Art of Motorcycle Maintenance


1985 K100RS (Sold)
2000 323i (Sold)
2003 1150GS (Sold)
2009 528Xi
2004 K1200GT
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post #5 of 5 (permalink) Old Apr 4th, 2013, 2:25 pm Thread Starter
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Location: Walnut Creek, CA, USA
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Thanks. I agree that I have a fuel problem. Interesting point about the fuel pump damper.

I haven't heard of the injectors being a problem on these bikes. Do you think that could be a cause as well?

Craig
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