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Thread: Starting Issues 1987 K100RS

  1. #1
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    Starting Issues 1987 K100RS

    Was wondering if I could get an opinion from the collective minds of knowledge regarding a recent issue. I'm riding a 1987 K100RS with roughly 43,000+ miles on it. Started it up yesterday to go in to work and it stalled out on me while down shifting. Went to restart, it would just turn over. Push started it, got it back to the house and let it run for a few minutes and turned it off. Went to restart it and nothing but the starter turning over. Put the battery on the charger, went to work, 9 hours later returned home, it started right up. Let it run for a while and shut it down. Went to restart and...nothing but the starter. I'm thinking alternator...anyone ever experience this before and can weigh in?

    Many thanks!
    Last edited by deilenberger; 03-03-2014 at 08:54 PM. Reason: added year/model to thread title

  2. #2
    A bozo on the bus deilenberger's Avatar
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    Dear gellermpd (real name?)

    Please review: http://www.bmwmoa.org/forum/showthread.php?46057 - I'll add that info to your thread title in the hope of enticing some people who might know something into the thread.

    As to your problem - is there a particular reason you're thinking "alternator" - is the red warning light not going out when the engine starts? It doesn't sound like a charging system failure to me..

    As to what the problem might be - lots of possibilities, and some diagnostics will be needed.

    An engine needs 4 basic things to run:
    1 - Fuel - need something to burn explosively
    2 - Air - provides oxygen to mix with the fuel giving a combustible mixture
    3 - Ignition - A source of ignition for the mixture
    4 - Exhaust - Someplace for the results of the combustion to go

    Typically - when an engine won't run - one of these has gone missing.

    To test for them:

    1 - Fuel. When the engine doesn't start - stop trying - pull a spark plug and look at it. If it's wet or smells heavily of gasoline, you have fuel. If it is bone dry and there is no smell - then figure out why you have no fuel getting into the cylinder.
    2 - Air. Unless you have a cracked air intake hose (the big one between the air filter housing and the intake plenum, chances are you have air.
    3 - Ignition. If the plug is wet when you removed it in #1 - then there is a chance you have no ignition. That results in a very rich mixture in the cylinder.
    4 - Exhaust. Sounds odd - but was called to help a friend once and found he'd plugged the exhaust with a big rubber washer while he washed the bike, and forgot to remove it. We'll assume this isn't the case with your bike.

    A question or two:
    1. When the bike does start up - do you allow the engine to reach operating temperature before shutting it down?
    2. Are you cracking the throttle or using the "choke" (actually a fast idle control) when trying to start it?
    3. What's the temperature where you're trying to start it?

    The reasons for these questions: When the engine starts up cold it starts with a very rich mixture. The fast-idle (aka choke) control adds intake air to the mixture by cracking the throttle bodies open a bit - allowing it to start. If the temperature is cold - the mixture is richer.

    Starting the engine and then quickly shutting it down can result in a way too rich mixture being left in the cylinders. If you go to start it again and it's still cold - an additional shot of rich mixture is added to what's already in the cylinders. In that case - the mixture can be too rich to start. If you let it sit for a while, some of the cylinders will have a valve open and some of the rich mixture will evaporate past the valves - sometimes enough to let it start next time you try.

    That's pretty much what I'd be looking at. If you can read a plug next time it fails to start - that would give us a good start on being able to point you at more specific potential problem points.. If it was me - I'd forget about the alternator. If the engine is cranking over - the battery is probably OK, and if the battery is OK and the red charge light isn't on - chances are the alternator is just fine. They aren't a real common failure point on these bikes.

    Given some of your symptoms - I'd consider also having a "load test" done on your battery - some of your description sounds like a battery on it's last legs. The amount of charge lost when starting - even with a perfectly functioning alternator can take 15-30 minutes of running at normal riding RPM's to replenish. Repeatedly starting it, stopping it and starting it again will cause a marginal battery to simply give up the ghost. Eventually - if you continue doing this - you'll be asking why the starter won't stop running even with the key off..
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  3. #3
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    Re: Starting Issues 1987 K100RS

    Thanks deilenberger! The real name is Jim Geller, gellermpd is an email I created at my first police department that I have been using for years. To answer your questions:

    1: Unfortunately, no. I was letting it run for a few minutes but shut it off.
    2: I use the throttle when starting the bike. Usually about 3/4 on and when the bike fast idles around 1000 rpms I shut the throttle off.
    3: Yesterday morning it was around 30 degrees in the garage.

    The red warning does go off when the bike is at idle. It's been sitting over night. I'll try and start it up tomorrow. If it doesn't kick over I'll check the plugs and report.

    Many thanks!
    Jim

  4. #4
    A bozo on the bus deilenberger's Avatar
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    Hi Jim,

    #1 and #3 make me think too rich a mixture making it harder to start, combined with a cold battery that may not be quite up to snuff = not wanting to start.

    I'll be interested in hearing what the plug looks like.

    Don
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  5. #5
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    Ok. Had the battery on the charger over night. Went downstairs, about an hour ago, unplugged the charger, no choke, key in and the bike started right up. I put the choke up to about 3/4 on, ran it until it fast idled, took the choke off and ran it for about 20 minutes (with no red charging light) while I shoveled a path to my car and cleared the snow off it. Came back to the garage and turned the bike off. Went to restart and nothing but starter noise. Plugged the battery back in to the charger, ran some errands for about 45 minutes, came back, unplugged the charger, and the bike started right up, ran for another 10-15 minutes, turned the bike off, went to restart, nothing but starter noise.

    Since everything is revolving around the battery being charged and the red charging light is not coming on I am now leaning towards the battery. I also noticed that when the bike is at idle the headlight is kind of dim, but when I throttle up a bit it brightens up. I never noticed it before with this bike or my MZ...is this normal?

    Again, a big thank you to all who have chimed in!

  6. #6
    A bozo on the bus deilenberger's Avatar
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    Quote Originally Posted by gellermpd View Post
    Ok. Had the battery on the charger over night. Went downstairs, about an hour ago, unplugged the charger, no choke, key in and the bike started right up. I put the choke up to about 3/4 on, ran it until it fast idled, took the choke off and ran it for about 20 minutes (with no red charging light) while I shoveled a path to my car and cleared the snow off it. Came back to the garage and turned the bike off. Went to restart and nothing but starter noise. Plugged the battery back in to the charger, ran some errands for about 45 minutes, came back, unplugged the charger, and the bike started right up, ran for another 10-15 minutes, turned the bike off, went to restart, nothing but starter noise.

    Since everything is revolving around the battery being charged and the red charging light is not coming on I am now leaning towards the battery. I also noticed that when the bike is at idle the headlight is kind of dim, but when I throttle up a bit it brightens up. I never noticed it before with this bike or my MZ...is this normal?

    Again, a big thank you to all who have chimed in!
    It's pointing to the battery to me - which is why I suggested a "load-test". Almost anyplace that sells batteries will be capable of doing this test. The test puts a big load across the battery, partly discharging it, then tests how long it takes the battery to recover. It will show up a dying battery rather quickly.

    When you say nothing but "starter noise" - can I assume you mean the noise the engine makes turning over, or just the starter motor spinning?
    Don Eilenberger http://www.eilenberger.net
    Spring Lk Heights NJ NJ Shore BMW Riders New Sweden BMW Riders
    '07 R1200R (current ride) and some bimmers.. and a Porsche

  7. #7
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    Possibly the Ground Cable

    I had an issue similar to this years ago with an '86 K75C. It turned out that the ground cable coming off of the battery was corroded within the insulation. Nothing visible from the outside: connections were good and clean as was the entire bike. Before you replace the battery, check that cable.
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '85 K100RS, '00 R1100RS

  8. #8
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    Well, got the new battery yesterday. Hooked it up and the bike cranked without an issue. Let it run for about 20 minutes and shut it down. Started right up again! That being stated, it was in fact the battery.

    Thank you all for the knowledge and pointers! Very helpful and now I am a bit more educated on this issue.

    Many thanks!!!

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