1986 125M no spark, kicking my butt, again

Discussion in 'Tech Area' started by waltinbatonrouge, Sep 6, 2018.

  1. waltinbatonrouge

    Joined:
    Jun 26, 2017
    Messages:
    34
    Likes Received:
    1
    Hello again!
    i Received the trike in shop with wiring harness a mess, (a bundle of cut/splice wires) 2 spare cdi's
    Customer ordered replacement wiring harness, i went through it, then installed it.

    everything works, lights, electric start etc except no spark. I have the factory service manual. and about 3 hours in the bike.
    heres what i've got, so far


    1st issue...all three cdi's ohm differently according to the FSM,

    However, i read on forums that the readings in the book are wrong, so there.

    when i measure the pulse trigger voltage with the min max feature on the fluke, ac output is .3vac
    is that too low or ok? im just not sure..Book doesn't say only provides resistance reading which checks out.

    output to coil from cdi is the same .3vac....so i guessed cdi bad. swapped with a spare. Now vac out to coil is 0vac.
    second bad cdi?

    the oem version of the honda cdi is out of stock and if it were its $140
    I could just spring for one of the pit bike cdi's on ebay, there are zillions of them with matching 6 ping plug/jacks and they are cheap enough, but...here's my dilemma

    i understand that there a 2 versions of the CDI, an ac version and a dc version. DC versions are larger like one of the spares i received with the bike. (see pics)
    some forum info says dc versions are for bikes with batteries others say differently. so which cdi does this bike use. .

    I'd really like to be able to isolate the problem by real troubleshooting rather than just wholesale replacing the cdi, pulse generator, and coil, but I;m at a standstill...
    Can anyone:
    confirm trigger voltage
    which cdi is the correct one, ac or dc?
    any other thoughts..thanks again

    walt
     
    #1 waltinbatonrouge, Sep 6, 2018
    Last edited: Sep 6, 2018
  2.  
  3. wanrep

    wanrep Active Member

    Joined:
    Jul 5, 2018
    Messages:
    115
    Likes Received:
    35
    I thought they only made the ATC125M's in '84 &'85.
    Both of those took the same cdi. The small one.
    I'm not clear on the ac/dc version but the exciter coil at the stator puts out ac volts which is rectified to dc in the cdi.

    Have you made sure the black or black/white wire (depends on year) at the cdi isn't grounded?
    It grounds at the kill switch & ign. switch.

    All my manuals are pre-peak voltage. Only have ohm values for the coils.
    Exciter coil 100-400 ohms
    Pulse coil 90 ohms.
     
  4. waltinbatonrouge

    Joined:
    Jun 26, 2017
    Messages:
    34
    Likes Received:
    1
    Hi Wanrep! thanks for helping here..
    Best i could find out, the 125M went through a big redesign in 86..new engine..(sent pic)
    Im hoping that the smaller cdi's with the 6 pin plug are interchangeable with the pit bike version i find on ebay...yet the picture in the FSM shows the larger version...
    I'm soooo confused...

    the pulse coil checks out resistance wise, but just not sure if the trigger voltage is high enough at .3vac to discharge the cdi to the coil.....i reset the coil gap and .014, per guess work, but it wasnt far off to start with.

    Unfortunately, the b/w wire isn't grounded out on this bike, i wish this one was that easy...
    any other thoughts more than welcome.
    thanks walt
     

    Attached Files:

    #3 waltinbatonrouge, Sep 6, 2018
    Last edited: Sep 6, 2018
  5. wanrep

    wanrep Active Member

    Joined:
    Jul 5, 2018
    Messages:
    115
    Likes Received:
    35
    My mistake...they did make them in '86 & '87 and yes, they were different from the older ones.
    I have some cdi's from an '86 TRX125 but it's a different part #. Weird.

    I know the peak voltage numbers from early '90's Z50, CT70 and TRX90 all say:
    Pulse coil - .7V minimum
    Exciter coil - 100V minimum

    What voltage are you getting out of the exciter coil?
     
  6. waltinbatonrouge

    Joined:
    Jun 26, 2017
    Messages:
    34
    Likes Received:
    1
    I sent along a schematic with the values..
    Bu/Y (Blue Yellow) to Gnd. .3vac when cranking- Resistance 336 (range 292-357)
    Bl/R (Black Red) to Gnd 37vac when cranking , Resistance 240 (range 100-300)
    Bl/W (Black White) to Gnd Open
    i did read on RMstators page that the gap for the pulse generator need to be close to ..010 i;ll tweak it in the am ..see if anything improves..

    Thanks again
     

    Attached Files:

    #5 waltinbatonrouge, Sep 7, 2018
    Last edited: Sep 7, 2018
  7. wanrep

    wanrep Active Member

    Joined:
    Jul 5, 2018
    Messages:
    115
    Likes Received:
    35
    The ohms are right where they're supposed to be for both coils but the cranking voltage is way low.

    I'm kinda grasping at straws but I've seen it, albeit only once in all my years.
    I had a Kawasaki with a no spark issue and the flywheel had lost most of it's magnetism.
    It would barely hold a screwdriver to itself. Replaced it and it had spark.
    Easy enough to check.

    I'll keep thinking.
     
  8. waltinbatonrouge

    Joined:
    Jun 26, 2017
    Messages:
    34
    Likes Received:
    1
    hmmm..ok flywheel seems to be "magnetized" attracts my screwdriver just fine, the pulse generator is actually pinned in place so i could not move it any more. ...rechecked the ground lead at the engine, broke 'em loose and retightened...and whoa...pulse output is still at .3vac
    but stator output effectively doubled to 70vac...double checked meter...yup..i know..

    Lemme see if i get any sparkle!
     
  9. waltinbatonrouge

    Joined:
    Jun 26, 2017
    Messages:
    34
    Likes Received:
    1
    ok tried the 3 cdis and new coil that owner had that tests fine...old coil was open in the prmary..still nada...so i broke down and ordered this...will be back then...whew!

    at least i get a little buzz from the 70vac...so it is getting there!

    thanks again

    Brand New Ignition Coil Cdi Set Honda Atc Xr Crf Trx 50cc 70cc 125cc 250cc 300cc
     
  10. waltinbatonrouge

    Joined:
    Jun 26, 2017
    Messages:
    34
    Likes Received:
    1
    hey wanrep...I've been doing some research...i should have the new cdi and coil today but i'm guessing that its the pulse coil...just a nasty feeling...back in a bit after the mail comes...thanks again..

    oops just installed new cdi and bingo the bikes running...
    i will post the values tomorrow..
    thanks again
     
    #9 waltinbatonrouge, Sep 10, 2018
    Last edited: Sep 10, 2018
  11. wanrep

    wanrep Active Member

    Joined:
    Jul 5, 2018
    Messages:
    115
    Likes Received:
    35
    All's well that ends well.

    FWIW...that pulse coil is the same one that Honda used on literally hundreds of different ATV's.
    They are canary priced...cheep, cheap.
     
    racerx likes this.
  12. waltinbatonrouge

    Joined:
    Jun 26, 2017
    Messages:
    34
    Likes Received:
    1
    hi again...i'm curious to see what that trigger voltage actually is on this rascal...when its running
    so i'll know next time..Ah yes! i did see the pulse coils for about $12.00

    i was so ready to push the ebay button!..thinking that of 3 cdis the owner had dropped off, at least one had to be good...
    and what else was there? new harness, flywheel that is magnetic..had to be the pulse coil? right? ..nope 3 bad cdi's...
    thanks again for your insight..i hear there is a 69 BSA rocket 3 on it way in with some weird electrical problems..

    can't wait..walt
     
    #11 waltinbatonrouge, Sep 10, 2018
    Last edited: Sep 10, 2018
  13. wanrep

    wanrep Active Member

    Joined:
    Jul 5, 2018
    Messages:
    115
    Likes Received:
    35
    OH GOD...Lucas (spookas) electrics...you're on your own, there...LOL
     
  14. waltinbatonrouge

    Joined:
    Jun 26, 2017
    Messages:
    34
    Likes Received:
    1
    yup lucas, prince of darkness aaaaawwwwwwoooooooooooW

    here are the values after we got it fixed and when the bike is running...
    pulse trigger 1.2vac
    stator output 83vac

    thanks again
     
    #13 waltinbatonrouge, Sep 10, 2018
    Last edited: Sep 12, 2018
  15. racerx

    racerx Administrator
    Staff Member Administrator

    Joined:
    Jul 10, 2005
    Messages:
    13,098
    Likes Received:
    1,169
    In Britspeak..."the Lucas curse":eek:
     

Share This Page