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Thread: Attempting to build my own CDI box......input?

  1. #1
    Join Date
    Mar 2007
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    Attempting to build my own CDI box......input?

    So.....my YT125 Tri-Moto needs a CDI, and I thought, hell, I'm a decent tech, I should be able to figure this out

    I've got my CDI box open and managed to scrape all of the silicone goo laced with little rocks away to an almost bare circuit board with components (I figured anyone that wanted to hide the components so well, it's GOT to be simple ), and I'm looking at one capacitor, a transistor, a diode, 3 or 4 resistors, and a mylar capacitor. Pretty simple if I can figure out what transistor is used.

    My plan is to scrape the remaining junk out, and create a schematic of the CDI and attempt to build it on a small universal circuit board and etch the board traces myself. Couple questions for those of you who might know:

    1. I assume that the advance for the timing is automatically controlled by the trigger pulse, and not by this transistor on any sort of curve? It's only four wires.....two ground, charge, and trigger.

    2. Is there a universal CDI or a cheap one that will work in place of what I'm trying to do? I just don't want to spend $145 for $2.00 worth of electronics. Aside from which, if I can build it functionally, with experimentation I can make it better

  2. #2
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    I've seen guys use Ford Duraspark units on ATV's. If they can use those you should be able to use a chevy ignition module as it's smaller.

  3. #3
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  4. #4
    Billy Golightly's Avatar
    Billy Golightly is offline Always finding new and exciting ways to not give a hoot in hell Catch me if you can
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    Interesting stuff! I'll be watching this thread closely.

  5. #5
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    I had a ford coil pack for my coil on my 250r and thats is far as I took it, it made stupid amount of spark, if you can make a universal adjustable cdi unit you just built a better mousetrap my freind.

  6. #6
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    Used

    Cant you find a used one? I think you might be in over your head. Ive never heard of anyone rebuilding a CDI. Goodluck if you do.
    3-85 ATC 70
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  7. #7
    atckowalski is offline Formerly "aaakowalski" Arm chair racerJust too addicted
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    I was just wondering the same thing. Here is a picture of the cdi off my Klt 200.
    Attached Thumbnails Attached Thumbnails cdi pic.jpg  
    1985 Ytm 225 dr (Black and gold)
    1984 Kxt 250 A1 Tecate
    1981 KLT200a1
    1983 Yt 175
    1985 Atc 350x
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    1985Ytz250 Tri z

  8. #8
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    ebay is your friend. problem solved
    83 ATC70
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    Lots of parts

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  9. #9
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    I give him alot of credit for contemplating it.

    Anyone who knows electronics (like my brother) finds this a challenge and would love to come up with an easy fix or a way to improve it.

    Buy a cheap used one to get running but please continue forwards with the project!!
    All our government does is distract us while they steal from us, misspend our tax $ and ruin our country

  10. #10
    Join Date
    Jan 2003
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    hey, honda cdi's are real reasonable, get one and wire it into the circuit. early 200x would probably do it.
    one cylinder is not enough!!

  11. #11
    Join Date
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    Buffalo, New York
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    Quote Originally Posted by Dirtcrasher View Post
    I give him alot of credit for contemplating it.

    Anyone who knows electronics (like my brother) finds this a challenge and would love to come up with an easy fix or a way to improve it.

    Buy a cheap used one to get running but please continue forwards with the project!!
    That's exactly what I'm doing

    But, with the thought that a used one might end up failing me in a most inopportune time at some point, I'm going forward, and here's what I've learned by bouncing ideas off of a couple people at work.

    The CDI is nothing more than a switching apparatus. On my simple application, it does nothing with the advance curve. The advance curve is calculated by the stator in the same way that the cam plates inside a distributor change the advance in a car work in conjunction with the vacuum advance.

    This being said, the charge side of the capacitor is always going, after viewing the schematics of the trike itself, the main power coming from what I'll refer to as the main power rail, which powers the headlights, etc. IN many such applications, the headlight acts as the voltage regulator of the system (it has in simple circuits in Honda scooters, but not in this case).

    Okay, so we've got about 5.86 VDC on the main rail and on the trigger circuit. Good. Now the problem is that in the link that dansvan posted as well as every other thing I've seen online assumes a 12V rail. Since this is 6V, I have to come up with something a bit different.

    Enter the GM 4 pin module. It has a trigger voltage of between 5 and 7 volts, around 6 being the optimum (as I read it). Great! So here's the module, a pic I grabbed off the net:



    The four HEI module terminals are labeled W, G, B and C.

    W = positive lead (+) from the pickup
    G = negative lead (-) from the pickup
    C = negative side (-) of the coil
    B = positive side (+) of the coil

    The base of the module must also go to chassis ground, so that should account for all of the major hookups. The next question is whether it will actually work

    Next, my plan, while still delving into the remains of my current CDI box, is to hook up the GM module in place of the CDI, and measure the exit voltage and pulse that would energize the coil to see if this actually has the potential of working. My only doubt in this regard is that since CDI relies on capacitance discharge, it would have to energize something I would think, and the GM module is nothing more than a switching diode.....the end result being a direct and applied +6V to the coil, but not at a set stored pulse. The advantage of the release from the capacitor versus regular "line" voltage would be not only in an even discharge but higher amperage (if my thinking's correct).

  12. #12
    Join Date
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    Totalling the components inside

    Looks like inside this CDI there are:

    (2) 100K ohm resistors
    (1) 150 ohm resistor
    (3) blue-banded diodes marked M1
    (1) red-banded diode marked IR
    (1) 3 lead transistor, light green in color, no identifying markings, similar to a 2N3903
    (1) capacitor, rated at 10 uF @ 16VDC
    (1) mylar capacitor of unknown value
    (1) tiny PC board, printed by Mitsubishi

    Total of (6) wire leads

    That's it! Time to hand a part of this off to a friend and resident electronics guru, and in the meantime attempt to create a schematic diagram of the unit. If I have a schematic, I can build them quite easily

  13. #13
    gravelord is offline At The Back Of The Pack Arm chair racerAt the back of the pack
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    bigger capacitor = more juice, more juice = good ............ no?
    resistors usually are to cut power - right ? so, in theory, bigger, im guessing, would restrict rev limit???
    dont quote me on any of this, except the capacitor one, that im sure of.. 90 percent... but a friend of mine used to be into electronics and make things - before he died. even built a big old frankenstein sized telas coil that shot lightning bolts ... well, no sense in trying to match a identicle to stock one. and honestly, even if you made one chances of it being as reliable as a aftermarket or stock one on the market, are probably not very good. (i take that back, probably wont be as as reliable as stock or the good aftermarket ones) but im all for trying things out, and for people to try to "do it them selfs" even if its just for the hell of it! its probably the first time someone tried to make their own cdi, go for it!!!!!!!

  14. #14
    Join Date
    Jan 2003
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    hey, I have a couple yamaha cdi's. what does yours look like?
    one cylinder is not enough!!

  15. #15
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    It's a small rectangular box, about an inch square by say 2" long, roughly.

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