AC-CDI v2.4

This ACCDI is EOL (end of live) and has been replaced by AC-CDI v2.6


  • For ONE or TWO* cylinders
  • Highly adaptable.
  • Can handle different pickups coils (Yamaha,Honda,Suzuki,Kawasaki,Zongshen)
  • Use the second pulse of the pickup for LOW RPM , idle and easy start.
  • Use the first pulse of the pickup for HIGH RPM, maximum power.
  • RPM when CDI jump from LOW to HIGH is adjustable.
  • LED indicator.
  • Need a working charging coil for the capacitor. (or a DC converter)
  • Doesn’t need a battery
  • No rev-limiter (Tested at 20,000rpm)


This CDI only does the ignition task, it doesn’t use any safety like neutral and sidestand.

  • Connect directly Neutral switch wire to Neutral indicator.
  • If you need “Side-stand security” then connect Sidestand switch to KILL wire of this CDI
  • Only works with VR pickup (Variable Reluctance AKA pickup coils)
  • Can’t work with Hall sensors or points.


  • How To wire this CDI?
  • How To hock this CDI on a Yamaha XT600


    How does it works?

    This AC-CDI use the 100 to 200 Vac provided by the charging coil to charge a capacitor through a rectifier bridge.

    When the pickup is triggered, the CDI turns on a thyristor that discharge the capacitor inside the primary coil.
    This burst of energy into the primary induce a high voltage of few thousand volts into the secondary coil, enough voltage to create a spark at the sparkplug contacts.

    Here is a interesting video description of how a CDI works.


    Switches positions


    This CDI doesn’t have seamless advance, it jump from LOW advance to HIGH advance.
    The moment when the CDI jump from Low to Full advance is adjustable by potentiometer RV2 (HI).

    Start tuning with RV2 at the maximum value (totally screw) then slowly unscrew it to lower the resistance, therefore the RPM where it switch.


    Compatible bikes

    Partially compatible bikes

    Not compatible bikes


    Click here for more info

    Step 1

    See: troubleshoot step1
    – Don’t connect the pickup(s)
    – Don’t connect the Kill Switch
    – Connect the ignition coil
    – Remove the sparkplug from the engine and connect it to a GOOD metal frame (ground)
    – Connect the charging coil
    – Connect a DC voltmeter between Ground and Kill output
    DIP Switches positions don’t matter for THIS step.
    – Kick start or electric start a few times to load the capacitor.
    The voltmeter should raise up to 100 or 200Vdc.
    If not: Check grounds, connections, joints, charging coil (stator)

    Step 2

    See: troubleshoot step2
    – DIP Switches positions : 1, 3 and 5 are ON. Other switches are OFF
    – Turn RV1 and RV2 to the minimum resistance (position: 0)
    – Kick start or electric start a few times to load the capacitor
    – Connect the +12v plug from a battery to the HI input:
    Led turns on.
    – Capacitor discharge into the ignition coil and one spark must fire at the sparkplug.
    If not: Check grounds, connections, joints, SCR, ignition coil, spark plug cables, spark plug.

    Redo this Step 2 but this time Connect the +12v plug from a battery to the LO input.
    Led never turns on when using LO input

    Step 3

    See: troubleshoot step3
    – DIP Switches positions : 1, 3 and 5 are ON. Other switches are OFF
    – Turn RV1 and RV2 to the minimum resistance (position: 0)
    – Kick start or electric start a few times to load the capacitor.
    When the main capacitor is charged and the voltmeter shows 100 to 200Vdc, then:
    – Connect the pickup coil to the HI input.
    – Kick start or electric start once.
    When the piston approaches the TDC and pass in front of the pickup, a positive pulse is send by the pickup and trigger the SCR.
    LED blinks and the capacitor then discharge into the ignition coil and a spark must appear at the sparkplug.
    If not: Check grounds, connections, joints, pickup coil, RV1 and RV2 are at 0, reverse the 2 wires of the pickup coil.


    Click here for more

    • Marty bought a 1984 wrecked XT600 without ignition and harness wiring.
      Got it running again even if it seems like he has some carbs works to do…
    • v2.2 fitted a Scooter:
    • Analog CDI on a DR125:
    • Analog CDI on a XT125/1982:
    • Analog CDI on a XT400:
    • Analog CDI on a XT600:
    • Analog CDI at 10,000rpm:

    • Analog CDI at 15,000rpm:

    27 thoughts on “AC-CDI v2.4”

    1. Hi Thierry
      Your circuit is an elegant solution to my problem, I am trying to adapt it the my S3800 Velo Solex, it gives my multiple option to try.
      Cheers Bill

    2. Hi Thierry
      I’m getting all of my components together and I noticed that the parts list and your picture of V2R4C2 don’t match, R1 And R4 hare different values, which is correct?

      1. Hi Bill
        Well spotted but it doesn’t matter, it depends on how bright you like the led…
        Beside I’m afraid you’re just wasting your time!
        As described above at “Ignition families“: MAGNETO IS NOT CDI !!


    3. hi Thierry,,,

      I just ordered for one off my friends this version the analogue AC-DC 2.4 version (via Ebay from you).. looking at the coil, I have a old one from a honda CX500 who had a old CDI type (12v) too… will that work ?
      The motor there is needed for is a xt600 from 1984.. no battery (for now :))

      ps. very interesting site,,, maybe on a later moment we go for the more advanced version but for now this is GREAT !!
      ps2. the original version on the Xt600 is more a AC version than the advanced one ?


      1. Thanks Marty,
        “an old CDI type (12v)” is very ambiguous! ACCDI don’t specify “12v” voltage as they are AC!
        Do you mean DC-CDI, TCI, points?
        in one word CDI boxes work with CDI coils type. Those coils have a primary winding from 0.3 to 0.7ohm.

        ps2: Original Yam CDI is more advanced than this analog AC-CDI. Advance timing is more gradual than my ACCDI v2.4

        1. hey Thierry,,, thanks for the comments… i’m expecting the package soon… and ambitious to start working with it ….. I ‘m experienced with electronics and worked with my bmw r26 on 3 phase generator (6 to 12v) and bought selfmade ignition… I hope that the Xt will start and run smoothly with this 2 step timing


    4. Hi Thierry
      This evening i did the first attempt to connect the AC-DCI… I need to check carefully… because i only have wires and everything else as connectior etc are gone 🙂

      my first simpel questions is; for a xt600 (43f) 1984…. 2 pickups ,,, only dipswitch 4 and 5 are on en the rest on off… is that right..

      I have a blinking led. when i kick the starter… but the motor does not run yet. no problem,,, the motor run on an Aliexpress scooter ignition, but the timing was totally wrong and not adjustable.

      but the carb is clean, the mouse is out of the airfilter. and for a simple start is the RV1 and 2 really important ? (for a XT600)? RV2 is on the max as required. RV1 i need to check

      thanks marty

    5. hey Th,
      just to be sure, not complaining 🙂 only asking and not ready yet with building and testing:)
      for the 3 steps I did not had the time, but will do 🙂
      have a nice weekend

      1. hi thierry,
        i’m happy,,, the xt600 with you AC-CDI works.. i have a few problems on the bike,,, I mean it is not complete… and the carbs are ultra-soon cleaned,,, maybe the adjustment is not yet correct
        but the engine runs,,, i’m really happy that i have a basis to work on


    6. 🙂
      I will buy and DC_CDI too,,,, I want to use that for the primary use, the ignition curve will be more then original. and I like to work on this 🙂

      But for now,,,, I can further work on the Xt,,, Need to check how to adjust the 2 adjustable Resistors. Need to read the “f…king” manual… but that is for later.


      1. Hi Th,

        I hope you are well. on this moment i’m replacing the exhaust XT600, so that i’m able to test some more stuff.
        I ordered some connectors, to replace straight connections on the wiring (missing) to the CDI unit in the small box,.

        I will solder the red LED to the outside of the box, what after some last adjustments will be filled with exoxy..

        My question is pro-active on the the RV2, I did not check how to adjust,,, and the the effect on turning the RV2. Due to the fact that i”m not familiar with the running/character of my bike (I bought it from a friend)

        Do you have any guidance on how to adjust the moment for static Low / High “moment” ?


        1. Hi,
          The easier way is to mimic the original behavior of the engine. But as you are not familiar with it you can adjust it this way:
          1) Rev the engine over 5000rpm
          2) Turn RV2 to position 4
          2) Disconnect the pickup LOW wire: Set the switch N°5 to OFF position . Only 4 is ON.
          3) Slowly decrease the RPM to 3000RPM
          4) Turn RV2 counterclockwise until the engine stop.
          5) Reconnect pickup LOW

          Now the CDI will jump frow low to high advance at around 3000rpm

          1. hi TH,
            only a short question on this description on point 3. is 3000 RPM the best RPM to switch to max timing advantage. I don’t have the experience yet in practice, but can imagine that with 2000, or 2500 RPM that already would work fine too ?
            yes official it is much higher in a nice curve… and this is a hard switch, what is fine… but when is the best moment…

            1. Hi marty,

              Yes it will works at 2000 – 2500rpm and you can have the feeling of more power but is bad for the piston.
              Too much advance will make the engine knock !
              It’s safer to follow the Yam original timing.

    7. hey thierry,

      yes , you are right… I don’t want to hear it … but yes… understand.
      on the moment I have a battery , and starting on the wiring of the bike.
      i’m in the market for the more advanced one,,, V10..
      we keep in touch,,,

    8. Thank you very much for engineering this Thierry. This is amazing as every single CDI on Ebay under $50 does not facilitate any form of pickup to pulse delay needed for many of these motorcycles.

      The XT225 uses the same engine as the TW200. It is my understanding they both use a timing advance of 9 degrees BTDC until 2000 RPM and then jumps to about 31 degrees BTDC by 6000 RPM. After it slowly retards timing to about 29.5 degrees BTDC at 9,000 RPM. It is clear the pickup pulse delay of AC-CDI v2.4 is exact and will not gradually advance or retard timing. Yamaha manuals claim there is a fast but not instant advance increase between 2,000 and 5,000 RPM and very gradual advance decrease from 5,000 RPM to 9,000 RPM.

      If the positive pick up is at 9 degrees BTDC and the negative pick up is as 60 degrees BTDC can RV1 be used to delay the pulse to 30 degrees BTDC? Of course we do not want 60 degrees of advance.

      I do not understand why we are choosing the off position for switch 2 for the TW200/XT225. There is 1 pickup so switch 1 is on. It is negative high RPM pulse so switch 2 should be on? It is positive low RPM pulse so switch 5 is on.

      Thank you very much for your time and knowledge.

      1. The long bar on the rotor of TW200/XT225 goes from 10 to 70°.
        the first rising edge of the bar gives a negative pulse at 70° for high rpm, the last and falling edge gives a positive pulse at 10°
        You can run the bike safely using only the positive pulse (but no advance as you may guess)
        If you go on switches 1,2,5 for a NP signal, you will use the 70° pulse, this one is “delayed” by RV2.
        The higher the trigger, the latter the spark (= less advance). Below a positive first pulse:

        RV2 may be too low to give 40° “delay”. A 47k should be better.

        1. Thank you Thierry. There are not many people in the world as wonderful as you to take the time to educate the world in this way.

          I may understand your words. RV2 is a variable resistor. It changes the resistance to the high voltage output by the trigger coil. By replacing RV2 with a 47,000 Ω resistor it will additionally increase the time it takes the trigger coil voltage to get to the BTA08-600B bidirectional triode thyristor (triac). Once the trigger gets to the BTA08-600B triac the L105J 400V capacitor will discharge into the ignition coil producing a spark closer to 30° BTDC. Resistors can be combined to change resistance value or use a 50k potentiometer to achieve advance required.

          Based on this information I will re-order the CDI. I apologize for my confusion. I hope this information means more people will buy your CDI module as they will understand they can modify it for their use.

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