Purpose of CDI
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Thread: Purpose of CDI

  1. #1
    Member ldw72120's Avatar
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    What does the CDI do? Why are they different on some models?

  2. #2
    Senior Member lizrdbrth's Avatar
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    The CDI system is the brains of the oufit, providing a spark and controlling ignition timing.



    Stuff changes. Hence the different components over the years. Sometimes things become more advanced and/or rel;iable, sometimes a new vendor can produce the same item more cheaply, and sometimes a vendor can do both.



    The verdict's still out as to which is the case on our bikes, but it's at least generally agreed that at least in terms of the CDI, gens 2 and 3 have been more reliable than was gen 1.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  3. #3
    Member ldw72120's Avatar
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    Quote Originally Posted by lizrdbrth View Post
    The CDI system is the brains of the oufit, providing a spark and controlling ignition timing.



    Stuff changes. Hence the different components over the years. Sometimes things become more advanced and/or rel;iable, sometimes a new vendor can produce the same item more cheaply, and sometimes a vendor can do both.



    The verdict's still out as to which is the case on our bikes, but it's at least generally agreed that at least in terms of the CDI, gens 2 and 3 have been more reliable than was gen 1.
    I have a 1987 (just purchased) and a 1995. The coil part number is the same but the CDI part number is different. Will the CDI from the 1994 work on the 1987? I have a few issues I'm trying to isolate to a specific part.

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    Senior Member rm_hm's Avatar
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    A long time ago another user "fourcycle " wrote



    Looking at the schematics for both the '87 and '88, the difference is how the coils are wired in the stator and the wires out of the CDI's. In the '87 the high voltage coil (red wire to brown wire) is in series with the timing coil (brown wire to gnd) In the '88 and later, the high voltage coil (red to gnd) is isolated from the timing coil (brown to yellow).



    One possibility might be to rewire your stator so that it matches the '88 and later stator as far as the ignition side is concerned. That would required breaking the common bond between the coils where the brown wire is attached, grounding the HV coil wire to the stator and adding a yellow wire to the other end of the timing coil. Now you have a place to attach your yellow wire and the ignition portion of '87 stator now looks like that of the '88 and later stator. That assumes that the number of turns of wire on the two coils didn't change between '87 and '88 and that the core CDI electronics didn't change either. I'd put it at a 75% chance of working.



    If you are willing to take the risk, you might also be able to make an '88 plus CDI work on an '87 by grounding the yellow wire. From looking at the two schematics, it's the only thing that might make sense to me.



    Then Tw87 wrote



    Good idea Fourcycle. On paper, what you propose makes sense. However, there's a hitch to it when it comes to implementing it. First of all, the high voltage stator winding (red wire) is extremely fine wire (hairlike). Secondly, the varnish used is very hard after 23 years. I know this because I changed mine out, and before I committed the $300 CDN to a new one, I made a valiant attempt to repair my old one. I was hoping that the coil winding had failed at the terminal where I could get to it and reconnect it. Well, I managed to remove the fly lead, and the little terminal from the varnish without (I thought) damaging anything else. However, once removed, I was unable to even find the loose end of the coil wire - it was that fine.







    Then later these topics came up http://tw200forum.co...87-with-94-cdi/ & http://tw200forum.co...nition-problem/







    Operose did a great cdi write up over here...https://tw200forum.com/index.php?/topic/2622-tw200-cdi/



  6. #5
    Senior Member operose's Avatar
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    The CDI from the '95 won't work to isolate parts on the '87 due to the amount of stuff you would have to change to make it work. This would not isolate potential issues, but rather create other areas for problems that would make it harder to track down the initial issue.



    Out of curiosity, what IS the problem that you are trying to isolate?



    My '91 is running great on a 2003 TTR125 CDI and source coil... It was an "easy enough" conversion but it would be best to verify the CDI system is in fact faulty before diving into something like that.



    If the system on your '87 is boned, I have a complete conversion setup that another member donated to me for the cost of shipping from thailand. This would upgrade the bike to later model electrical system and I would be willing to part with it for what I paid plus shipping to you.
    ITCB

  7. #6
    Senior Member lizrdbrth's Avatar
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    Dood, where you been?



    Riding, I hope.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  8. #7
    Member ldw72120's Avatar
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    Quote Originally Posted by operose View Post
    The CDI from the '95 won't work to isolate parts on the '87 due to the amount of stuff you would have to change to make it work. This would not isolate potential issues, but rather create other areas for problems that would make it harder to track down the initial issue.



    Out of curiosity, what IS the problem that you are trying to isolate?



    My '91 is running great on a 2003 TTR125 CDI and source coil... It was an "easy enough" conversion but it would be best to verify the CDI system is in fact faulty before diving into something like that.



    If the system on your '87 is boned, I have a complete conversion setup that another member donated to me for the cost of shipping from thailand. This would upgrade the bike to later model electrical system and I would be willing to part with it for what I paid plus shipping to you.
    The bike wasn't cranked for four years when I bought it. The previous owner said it sat for years before he bought it. It only has 2500 miles on the odometer. He said it was hard to start and often would quit running after and hour. He thought it was the carburetor and bought a new one and installed with the same result. I finally got it running but the idle runs up and down with no throttle input. Maybe 800RPM to 2000RMP. Sometimes it will backfire. I swapped the coil out between the two bikes and it seems to make it easier to start. I started it and rode it about 45 minutes Sunday night with no problems and last night it would crank and run, but would not rev up or continue to run. Possibly the CDI? I am sending a PM about the kit you have.

  9. #8
    Senior Member lizrdbrth's Avatar
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    Get a timing light and you'll know for sure what's happening the first time it stalls.



    I'd do a sticky on this, but no one would read it



    Get an old induction timing light. Cut the battery clips off and wire it direct to the battery. Mine has a battery tender plug permanently wired to it. Do whatever you gotta do to keep it connected while riding the bike.



    Rubber band the trigger so it stays on all the time and aim it somewhere where it won't blind you, then ride the bike til it pukes out on you, keep the throttle WFO and watch the light while it rolls to a stop, bucks, or whatever it's doing at the time.



    Light on and steady with rpm as you roll= carb or fuel problem.



    Light off or intermittent as you roll= ignition problem.



    It's a wasted spark system, so it'll fire twice every cycle. If it's messing up you'll have no trouble seeing it.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  10. #9
    Senior Member operose's Avatar
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    Quote Originally Posted by lizrdbrth View Post
    Dood, where you been?Riding, I hope.


    Ja, getting some riding done eh. Bought the bike in late june, didn't get it on the road until july, it was broken for over a month, and still managed to get 1600 miles in so far (yea yea, not a lot to some of you guys!) I poke into the forum once in a while still to see how things are going for everyone, but have been pretty busy with work and preparing for winter and stuff.







    Quote Originally Posted by lizrdbrth View Post
    Get a timing light and you'll know for sure what's happening the first time it stalls.I'd do a sticky on this, but no one would read it Get an old induction timing light. Cut the battery clips off and wire it direct to the battery. Mine has a battery tender plug permanently wired to it. Do whatever you gotta do to keep it connected while riding the bike.Rubber band the trigger so it stays on all the time and aim it somewhere where it won't blind you, then ride the bike til it pukes out on you, keep the throttle WFO and watch the light while it rolls to a stop, bucks, or whatever it's doing at the time.Light on and steady with rpm as you roll= carb or fuel problem. Light off or intermittent as you roll= ignition problem.It's a wasted spark system, so it'll fire twice every cycle. If it's messing up you'll have no trouble seeing it.


    Yup, pure awesome. You should make a sticky, I'd read it
    ITCB

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