85 K100RT Running & Electrical Problem - K-Bikes.com - Excellence in Motion
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post #1 of 5 (permalink) Old Mar 22nd, 2011, 12:48 pm Thread Starter
Join Date: Jun 2010
Location: Hoffman Estates, IL, USA
Posts: 3
85 K100RT Running & Electrical Problem

I have an 85K100RT (one owner-36K miles) new to me 2 years ago. It had been sitting for years. My bro-in-law got it going, professionally painted it and it became mine. Had a BMW independent shop go through it just after purchase and everything was fine except a faint glow in the alt. light (kinda normal). It stranded me once with a clogged fuel filter, but other than that all good.

Haven't ridden it much since last July and am trying to get it going again. Last July issue was similar to the clogged fuel filter. The bike had gotten really low on fuel, after I filled it up it would not restart. Waited and tried, waited and tried, finally turned over but ran really rough - got some techron inj. cleaner into it and road the 200 miles home the next day. Bike would not idle well and starting was questionable.

Pulled the filter and fuel pump. The screen had become detached from the fuel pump, filter may be and issue, so replaced the filter and pump. Used a vacumn pump to clear what little debrie that was in the pump sump out. s/b all good, but still would not start, starter stuck on, pulled the ground to stop it and replaced the relay then charged the battery. Starter sticks on again, crack green starter knob, replace relay, charge battery (yuasa 1 yr old). Starter sticks on again, replace relay, battery, right hand bar switches, fresh fuel.

Bike starts, but idle a little dicey, alt light glows, glows brighter on and off when revs up. Bike dies, restart and idles like crap, dies, starter stuck on.....

Go through the bike and clean all electrical contacts (thx don e.) Take the starter apart and clean the carbon out (thx). Replace the plugs with OEM (old ones-NGK-not bad). Check starter relay with continuity tester - not frozen, but may have freed up when contacts cleaned.

So, before I put the tank back on - is there anything else to check? I really like this bike and at this point have about $4K invested between purchase, go-through and this adventure, so thinking keeper if it will just run.


mjlough is offline  
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post #2 of 5 (permalink) Old Mar 22nd, 2011, 3:16 pm
PsyKotic Waterfowl
Join Date: Aug 2006
Location: Seattle, WA,
Posts: 1,328
Just guessing but either a coil going or an air leak. That's pretty low miles for a coil to go but 25 years???

With the bike idling spray some starting fluid around the rubber boots between the throttle bodies and the cylinder head. If the revs go up then one or more of those boots are leaking and need to be replaced.
FlyingDuck is offline  
post #3 of 5 (permalink) Old Nov 17th, 2011, 6:19 pm Thread Starter
Join Date: Jun 2010
Location: Hoffman Estates, IL, USA
Posts: 3
Update - still not starting

Update from March - put the bike back together and it still would not start. Same as before, it tries, on the third or fourth attempt the starter will keep cranking until the ground wire is disconnected. When this has happened previously I have gone in and replaced the starter relay (5th time). This time I waited overnight, recharged the battery, reattached the ground wire (no cranking after the pause) and let the bike sit all season while I put 10K on the other two.

I lurked around the forum and recently pulled the tank off again to replace the clutch interlock switch because it has not been replaced before. Tested the old one and zero ohms resistanc so not the problem.

Will put the bike back together tomorrow and try again.
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post #4 of 5 (permalink) Old Nov 17th, 2011, 6:25 pm Thread Starter
Join Date: Jun 2010
Location: Hoffman Estates, IL, USA
Posts: 3
Need a shop in the Bay Area

I am relocating to the San Francisco area - East Bay.

The K is going with me. I need a recommendation for a shop (quick). The shipper is picking up the bike tomorrow afternoon and I would like to just send it directly to the shop.

After countless hours of throwing parts at the problem it is time to get it to a pro.

Is there an independent or dealer in the bay area that is especially good with 2V K bikes?

Thank you all for the support. I apologize if my frustration sometimes leaks onto the page. I really like this bike, but it is the only one I have ever had that I could not trust to get me home.

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post #5 of 5 (permalink) Old Nov 17th, 2011, 11:16 pm
Join Date: Jul 2008
Location: Houston, TX,
Posts: 259
Check your injectors.

This is a better forum for k100 problems.

look at the bottom of the page:
"Other interesting links:"
There are a bunch of troubleshooting guides.

2007 Bmw k1200GT (My Vroom Bike)
1995 BMW k1100lt (Sold) (My mini-bus)
1998 BMW k1200rs Taxi (Sold) (Didn't get to say goodbye)
1986 BMW k100rt (My classic and first, Restore in Progress)
CGHEMWICK is offline  

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