DAX spark problem

Discussion in 'Honda CT70/Z50 Registry' started by Casey Neiman, Feb 12, 2020.

  1. Casey Neiman

    Casey Neiman New Member

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    I have a 1970 CT70 HK0 that I am having spark problems with. I am not a good Mechanic but am learning and enjoying working on this one. I replaced points and condenser, coil and plug. I tested spark with a voltage probe that lights up and a meter. The probe lights up at the output wire from the mag and at the input to the coil but not at the plug cap. I do show a bit over 100 vac at the cap but plugs will not fire. HELP.
     
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  3. racerx

    racerx Administrator
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    If you don't have a battery connected, your primary ignition circuit is open. There's jumper lead in the 4-pin battery connector; Honda did this to prevent people from blowing bulbs. The battery is the system voltage regulator; without it, voltages skyrocket.

    For testing purposes, I'd suggest unplugging the stator from the main wire harness, then running the HT coil input to the primary coil output from the stator. If you get spark, look downstream in the wire harness. If you still don't get spark, time to verify point gap and, possibly, condition of the HT coil. Coils rarely fail. Thus it could be a problem with the condenser; doesn't sound like it, though, based on your reported test result. Start with the easy stuff...we can always go into additional steps, if needed.
     
  4. Casey Neiman

    Casey Neiman New Member

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    I have around 5 vac at stator wire and 110 vac at plug cap so I thank no this means the coil is working. No battery on machine but I hooked the red and blue wires together at the plug. I had spark for a few cranks at first try before changing points and condenser and coil but it went away and hasn’t returned. Good ground on the coil.
     
  5. racerx

    racerx Administrator
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    I'm inclined to agree that neither coil has failed. It takes more like 10kV to get a spark to jump a plug gap but, getting that requires a minimum rpm, even when kicking-over the engine. It also requires that everything is working properly. At this point, I think you've narrowed things down to points or/and condenser. Next step, try cleaning the points. Start by running a piece of of "shirt cardboard" between the contacts, followed by a shot of solvent (brakleen works well), then 2-3 passes using 600-grit (or finer) sandpaper and then a final shot of solvent. If that doesn't do it, not much choice but to try throwing another condenser at it. Condenser quality has slipped over the last decade, once in a while someone gets a defective part. It's also possible to kill a new condenser while soldering the lead, unintentional overheating is easy and, we've seen more examples of this than condensers that were defective.
     
  6. Casey Neiman

    Casey Neiman New Member

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    Points and condenser are new but I may have overheated the capacitor. I will check the gap again then if that is good I will try a new condenser. Thank you
     
  7. racerx

    racerx Administrator
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    It's not just the point gap. It takes next to nothing to foul a set of point contacts, killing spark output. Some replacement sets have a protective coating on them, ostensibly to prevent oxidation; that's gotta be cleaned off...or you'll end up with what you now have.
     
  8. Casey Neiman

    Casey Neiman New Member

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    Thanks very much. I now have spark, it was the points. I had them set way off. Now if I can get it to run!! I sprayed just a touch of starter fluid and had flames coming out of the exhaust hole but won’t start
     
  9. cjpayne

    cjpayne Well-Known Member

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    Check the timing.
     
  10. racerx

    racerx Administrator
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    This refers to cam timing, verify that the index marks align properly.

    If this engine has a 4-speed alternator (spark advance mechanism) it's possible to install it 180-degrees off...a.k.a. "backward". If this engine has fixed spark timing, the ignition cannot be disassembled and thus wouldn't need to be checked.
     
  11. Casey Neiman

    Casey Neiman New Member

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    I had the timing 180 off. Fixed that, great spark but won't run. Little bugger keeps flooding, New carb.
     
  12. racerx

    racerx Administrator
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    I'd try to fix the carb, rather than just throwing another one at it. Flooding means it's getting excessive fuel, far easier to correct than the usual lack of fuel flow with vintage carburetors that sat for eons, improperly stored.

    Check the needle & seat assembly for missing parts, dirt. Then verify & adjust float level as needed. Set the pilot airbleed screw 1.5 turns out from seated and raise the jet needle C-clip two, or three, groove higher. That should lean things out in a big way...with no out-of-pocket cost and no time spent waiting for parts.
     
  13. Casey Neiman

    Casey Neiman New Member

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    It is a runner!! Started over...again and went through from the start. Fired up and runs pretty smooth but smokes. I am going to get some new rings for it. Thanks so much for the help, I had only the basic idea of what I was doing
     
  14. racerx

    racerx Administrator
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    Sounds to me like this engine needs a rebuild. Smoke usually means the rings aren't sealing well...scored/pitted cylinder walls. I would expect to find the intake port blackened...meaning a leaking valve and time for a valve job. This is garden-variety stuff for a ~50 year old engine.

    While you're at it, may as well split the cases, for a thorough cleaning & inspection. The shift forks are likely worn. Now's the time to replace them, + their pins. Thrown-in a new set of clutch discs & case screws and...voila!...first-rate rebuild, ready for another 4-5 decades.

    BTW, best to have the cylinder overbore determined before ordering the new piston & rings. I'd want to know what the finished bore size will be...could be anything from standard to fourth O/S. It all depends upon the amount of taper (wear) and depth of any scoring/pitting, if present. If you're looking for a little more power, a 52mm (88cc) bore-up kit can be had for the same money as overboring the original cylinder.

    IMO, better to go completely through an engine, leaving nothing to chance. It's cheap insurance.
     

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