R100 Ignition Question

Discussion in 'Airheads' started by 00_Green, Feb 27, 2012.

  1. supershaft

    supershaft because I can

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    You might just be describing the difference between 9.0:1 CR (I think that is what a '77 R100S has?) and 8.2:1 in the '81? If the S is single plugged there's a good chance that if you jetted the '77 to where you needed the choke more it would return the favor by pinging. Our shop had a lot of owners of then new 9.0:1 CR bikes lower their compression for pinging in the late '70's. You could always raise the compression in the '81. If I wanted more power than the '77, I would much rather start with the '81 but that's just some of us out there. But then again, you could have a problem like weak coils or any number of other possibilities. A blue spark in thin air doesn't really tell you. Good luck 00 Green. This is just the type of thing that is you just have to figure out.
    #21
  2. Wirespokes

    Wirespokes Beemerholics Anonymous

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    I've found it can take 500 to 1000 miles for a long-hybernating bike to return to full strength. During that period you'll find the settings frequently changing - carb synch going out, idle changing, rough running, etc.

    As weird as it might seem, it takes more effort for the plug to spark under compression than atmospheric pressure. I've heard a good way to test that is to run the plug wire to a spark plug that is then grounded to the one in the head. You'll have two plugs in series with one in the open, the other in the combustion chamber. Then watch the spark to see what's really happening.

    I've yet to try this, but know a guy who tests them this way and swears by the method.
    #22
  3. supershaft

    supershaft because I can

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    The best way to test that ignition IMO is to swap the coils, wires, and caps from the '77 onto the '81. It's easy and it's done.
    #23
  4. 00_Green

    00_Green Adventurer

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    All good points, we have tweeked the carbs after the last ride. I like the idea of swapping the coils, wires, and plugs!
    #24
  5. ericrat

    ericrat Long timer

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    It is a red letter day!:lol3

    Kindest regards,

    Eric
    #25
  6. 00_Green

    00_Green Adventurer

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    Wasn't that quoted out of context? I'm just saying ................. :rofl
    #26
  7. supershaft

    supershaft because I can

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    Exactly 00! :lol3 I sometimes agree with whole Bum sentences but rarely a paragraph in whole. In this particular case just one small part of a sentence! The guy reads like a FAA bulletin. While saying five things at once if you focus somewhere in the middle of the article you CAN get the jest of it. I disagree with him on this topic as a whole but I am trying to find something good in there! :lol3 I mean, his advise works but it is so easy to do better in this case.
    #27
  8. wirewrkr

    wirewrkr the thread-killer

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    Coils from A points bike to any electronic ignition bike???
    Not the best of your advice.
    #28
  9. 00_Green

    00_Green Adventurer

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    Believe it or not I did think about that. I don't know their physical size is the same or even similar but i would have checked part numbers and compaired primary and secondary resistance values before swapping.
    #29
  10. wirewrkr

    wirewrkr the thread-killer

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    Yeah, don't do it. Trust me.
    #30
  11. supershaft

    supershaft because I can

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    Thanks wirewrker! I forgot that it was an '81!
    #31
  12. supershaft

    supershaft because I can

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    What is the combined dual coil primary resistance as wired on the electronic bikes? I can't remember right now.

    Keep the primary as high or a little higher than stock and I still think swapping components is the only real test for ignition.
    #32
  13. kaput13

    kaput13 gasoholic

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    Another possibility you might want to double check (info courtesy of the Bum here by the way!:1drink) is to check whether the enrichener parts are on backwards. I know you say the carbs were carefully rebuilt but this is easy to do. In fact I was experiencing similar issues recently that you are describing until I found my mistake. At any rate, good luck, hope you solve it.
    #33
  14. bereahorn

    bereahorn Long timer

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    :lurk
    #34
  15. 00_Green

    00_Green Adventurer

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    I'm familiar with the enrichener info on Bums site. I had to read it a few (or more) times before I completely understood it. The enricheners were inspected and verified to be assembled properly while taking the carbs apart. They were inspected and reinspected after replacing the shaft orings to verify they were re-assembled right.

    I'm still working out of town but hope to get home tomorrow and back on it.
    #35
  16. bgoodsoil

    bgoodsoil Dare to be Stupid

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    Your location says Atlanta & Memphis, is the bike in Atlanta? It sounds like you've got a handle on this, and I'm no expert, but maybe another set of eyes would be helpful. If nothing else, I've got a coil and plug wires we could swap out to eliminate that from the equation. Gimme a call, 678.469.3298.

    -Brad
    #36
  17. ignatz72

    ignatz72 call me iggy

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    If the bike is in Memphis I'd be happy to offer another set of eyeballs/ears, etc.

    I agree with Wirespokes that dormant bikes will take some miles to "relax" again. Just went through that with my 93 GS (and previously my 83 RT).
    #37
  18. 00_Green

    00_Green Adventurer

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    Gents, Thanks for the generous offers to assit. Brad, the bike is in Atlanta. I live in Fayette County but work in Memphis. I may take you up on the offer Brad, I'll look at it again today and will probably be in touch.

    Thanks again!!
    #38