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Thread: Very strange spark issue!

  1. #1
    Registered User beano08's Avatar
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    Very strange spark issue!

    Hi all, new to the forum. I'm excited to be able to pick the brains of some very knowledgeable people.
    I was trying to diagnose an intermittent dim charging light, one that would flicker as I played with the rpm. I was checking connections everywhere, pulled the diode board and replaced it with no trouble. The bike started and ran fine AFTER I put everything back together but with the front cover off. Here's where things get strange; after I replaced the cover (I pulled the neg cable) I get no start. I check for spark and there's none. I pull the cover to trouble shoot and BAM spark! I've been able to reproduce this several times. For some reason, with the cover installed I get no spark. Now I'm far from a mechanical expert, but this just makes no sense to me. Has anyone heard of this before? I'd imagine the cover is somehow grounding something out, but I'm almost certain everything is back to where it's supposed to be.

    Any help would immensely appreciated!

  2. #2
    Registered User toooldtocare's Avatar
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    Most likely a pinched wire under the coverís lip. Pull it again and follow each wire. Especially around the top near the diode board, and the bottom near the points/bean cam. Looked for a wire mashed flat with the insulation missing.

    Let us know what you find. A picture would help too.

    Wayne

  3. #3
    Liaison 20774's Avatar
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    ^^ What he said!

    Welcome to the forum!
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
    Registered User beano08's Avatar
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    Thanks for the quick replies! I feel welcome already. That's what I had figured, I'll double check things tonight and get a picture posted.

  5. #5
    Rally Rat 1074's Avatar
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    pinched wire

    Most often the points wire gets pinched coming out of the points housing. If you put the cover on with the wire pinched you'll find resistance when aligning the cover flush with the engine. You might want to insert the rubber boot thingy into the cover before pushing the cover into place. It tends to stay in the cover better than just pushing it onto the front of the engine.
    Boxerbruce

  6. #6
    Registered User ebeeby's Avatar
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    Quote Originally Posted by 1074 View Post
    Most often the points wire gets pinched coming out of the points housing. If you put the cover on with the wire pinched you'll find resistance when aligning the cover flush with the engine. You might want to insert the rubber boot thingy into the cover before pushing the cover into place. It tends to stay in the cover better than just pushing it onto the front of the engine.
    +1
    1973 R75/5

  7. #7
    Registered User beano08's Avatar
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    Well you all were absolutely right! The wire leading to the timing mechanism was being pinched. Going back to my original problem, the charging light...
    My problem started after a longish 200 mile trip. I stopped to get gas and had no electrical at all. Totally dead battery. I was able to jump the bike and limp the remaining 60 miles home. She actually died pulling into the driveway, bless her metal heart. After charging the battery I get a dim charging light that I can get to flicker brightly and sometimes even go off by playing with the revs. I've done a fair amount of research and I think I understand the airhead charging system well enough. But can anyone point me towards a likely culprit? I feel like the fact that I was able to limp home on a dead battery and the slightly flickering nature of my charging light must point to a bad connection somewhere? I've checked all connections under the front cover and they seem reasonably secure.
    Thanks again, this is an amazing resource

  8. #8
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    Check your brushes (for wear), and rotor and armature (each for continuity), in that order. That's a good starting point. Good luck and good on you for sorting out your ignition problem.
    Gary Phillips - #6322
    Wildland Firefighter, Retired, Riggins, ID
    Heartland Moto Locos BMW Riders
    '77 R100/7 Dirt Hack, '83 R80ST, '85 K100RS w/EML, '00 R1100RS

  9. #9
    P Monk
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    my experience with old charging stuff

    my problem started in the driveway on a trip to a vintage rally. Gen light came on, that is why it pays to have two bikes. So I replaced rotor. Which was shot. Things worked well for a while then started getting problems again. This time it was the stator. Worked for a while then started getting intermittent gen lights after bike ran a while. If you guessed diode board you would be correct. Don't know how old your bike is but mine was built in 1973. All these parts won't last forever. I wish I had replaced the whole charging system the first time. Would have saved a lot of work. And for a little more $$$$ you can put and Alpha ignition in and never have to fool with points again.
    P. Monk
    74 R90/6 (the Black Hole) Harvey couldn't kill it. . 09 R1200 GS, drowned in Harvey replaced by 2011 R1200RT. Wife, 1953 model survived aplastic anemia and a bone marrow transplant.

  10. #10
    Registered User toooldtocare's Avatar
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    Glad you found the pinched wire. Now for the charging part. First, it probably is not the issue, but I have seen intermittent/weak batteries or bad connections give all sorts of symptoms. To eliminate the battery, do this. Fully charge the battery. Take a voltmeter reading. Immediately after taking it off charge, the voltage is normally 13.2 or 13.3. This is not an overcharged battery, but one that has a surface charge.

    Next, turn on the bike so the head light will provide a bit of load. Leave it on for one minute and note the voltage drop. After about a minute record the value. Should take off the surface charge and settle around 12.3 to 12.5 volts with the ignition and headlight still turned on. Turn off the ignition and wait another minute or two. The battery should recover to around 12.7 to 12.8 volts.

    Last step, start the bike and monitor the voltmeter. The voltage will drop to about 11 volts while the bike is cranking. Once started, it should settle out to about 12.6 or so at idle. Now rev the bike to about 3,000 RPMs. Watch the voltmeter. A good charging system should show about 13.1 to 13.3 volts.

    If the battery tests pass, continue to test the charging system. If it does not, replace the battery.

    Many things can lead to charging issues, including a burned out bulb in the charger indicator. We know that is ok, or it would not be on. Other areas to look at are the brushes, the diode board (you already replaced), voltage regulator, alternator itself.

    Kurt can probably provide you with links to other sources that will walk you through the troubleshooting process. Also, if you have access to a Clymer manual, Chapter 8 will walk you through the charging system pretty well.

    Good luck,

    Wayne

    PS. I don’t know where you live. We are having an Airhead Tech Day Saturday near St. Louis. I am driving there from Florida tomorrow, arriving Thursday. If you are close you are welcome to join us. PM if you are interested and I’ll give you more information.
    Last edited by toooldtocare; 10-17-2017 at 02:53 PM.

  11. #11
    Registered User ebeeby's Avatar
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    First thing I do when troubleshooting a charging problem is throw the battery in the Mississippi River. A shorted cell (which can easily occur from vibration on a 200 mile trip) can still show a good surface charge. A load test - preferably with a load tester- will expose the culprit, though most do not have a load tester on hand.
    Batteries can short out early in life, and sulfated plates can fail the system late in life.

    Every failure but one I have (personally) encountered has been the battery.

    Just sayin'
    1973 R75/5

  12. #12
    Registered User beano08's Avatar
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    I can't thank everyone enough for their guidance. I've heard battery is a common culprit, unfortunately that isn't my issue. My old battery tested good and the shop actually misplaced my battery so they kindly gave me a new one as a replacement. I've spent a fair amount of time reading about charging, and I think I know what needs to be done. I guess my question is; do my symptoms stand out to anyone? For example my gen light comes on slowly when I switch on the ignition. It's not instant like the oil and neutral lights. Also the fact that playing with rpm can get the light to flicker seems important to mention. Finally, to clarify I didn't replace the diode board, I just removed it and checked connections.

  13. #13
    Liaison 20774's Avatar
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    I'd be checking all electrical connections for corrosion, especially those associated with the charging system. The flickering of the charge light could be that the brushes are short and/or they're bouncing resulting in intermittency. Be sure that the snail spring which pushes the brushes down the commutator are not hung up on the brush holder...that happens when they get short and/or the brushes are replaced without properly configuring the springs.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  14. #14
    Registered User beano08's Avatar
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    ok, I'm going to start with the brushes I think. Doesn't an open rotor cause a non gen light? Can I eliminate that?

  15. #15
    Registered User toooldtocare's Avatar
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    Time to do some troubleshooting. Read this for a start. http://bmwmotorcycletech.info/trbleshootalt.htm

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