CT70 basket case - no spark

Discussion in 'Tech Area' started by RDRider, Mar 22, 2020.

  1. RDRider

    RDRider New Member

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    My son finally wanted to drag a 71 CT70 out of the barn that was given to us. No background was given to me about its issues. Before I decide to put any money into it I decided to check the basics.

    Spark - I was given no keys, so i could not turn the switch to on. Kicking the engine netted no spark, but oddly pushing in gear would, but only for a moment. I jumped every possible combination on the back of the start switch, but still no spark kicking. Spark plug is new. Wire was a wreck and needs replacement. 20200322_165357.jpg
    I pulled the flywheel and the points look perfect.
    Under the seat, the battery is gone and this is what's left of the terminals:
    20200322_164831.jpg
    Here is what it looks like at the battery terminals to harness. Is it normal to have the black ignition wires jumped?
    20200322_165816.jpg
    Here is the start/lighting switch. I presume it is in off, one is start, two is lights and start. 20200322_164839.jpg 20200322_164839.jpg
    I normally wouldn't buy or invest in anything this far gone, but I thought it would be a good learning experience for me and my son. Any advice to get this electrical issue sorted out will help motivate us to resurrect this gem!
     
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  3. PurplePackFan

    PurplePackFan New Member

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    Welcome to Lil Honda and congrats on taking on the task of getting this bike back on the trail!
    First of all, that black loop on the battery pigtail HAS to be there for the engine to get spark, with or without battery. These engines will run without a battery installed. Second, I would try pulling the fuel tank and removing the key switch as it appears to be in the OFF position. Some people run these bikes with no key switch at all so I think it is possibly shutting off the spark in that posirion. Also, the housing of the switch needs to be grounded to the frame, which it will be if it is attached properly with the threaded ring. Try for spark with the switch removed first. Third, you can probably get a key for that switch, if you decide to put a little $$ into ths project. Go to ebay: https://www.ebay.com/itm/Honda-Motorcycle-Keys-Cut-to-Code-Replacement-Spare-New-Ignition-precut-Key/182917157822?
    Fourth, if you have enough high tension spark plug wire, cut off the very end so it is square and the metal screw-like prong in the spark plug boot will literally screw into the center of the wire which should improve the high voltage circuit to the plug, should there be any.

    I'm no expert on these machines like others on this forum are, but hopefully this can get you started while others chime in. I've rebuilt a few of these and have gained a lot of knowledge and experience the hard way and this forum has made it much easier. Don't be afraid to ask.

    Good luck with your project and we'll be watching.
     
    OLD CT likes this.
  4. RDRider

    RDRider New Member

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    Great advice and info. Thank you.
    How would I unplug the key switch? I took the tank out and I can't get the wiring harness out far enough on either end to unplug it. I can barely reach inside the frame with my hand to the connector. Do I simply pull, or us there a tab to release?
     
  5. RDRider

    RDRider New Member

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    BTW, shouldn't I be able to jump contacts on the back of the key switch and get spark? If so, should the key switch body be in contact with the frame?
     
  6. kirrbby

    kirrbby Well-Known Member

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  7. CollegeCrankCase

    CollegeCrankCase New Member

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    If the key presents a difficult challenge, I have had success in the past by picking my own CT70 lock.

    Unwind a paperclip and just wiggle in as much as you can to try to fit the grooves. Then use a flathead to jimmy it to the other stations of the lock. Takes about 5-10 minutes and saves you an hour of shimmying out the fuel tank.
     
  8. racerx

    racerx Administrator
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    The plug wire looks worse than it really is. Clip it back 0.250-0.500"...just enough to get a clean end; the plug cap should screw right on. Then, you're good-as-new, the lead is just a little shorter than it was. Be forewarned, it's very easy to overtighten the plug cap on the wire.

    As for the intermittent spark, that all but eliminates the wire harness, including the keyswitch, as the underlying problem. You can unplug the stator from the harness then run a test lead from the black primary ignition coil output to the secondary/HT coil input (which has to be unplugged from the harness) and then you've bypassed the wiring & keyswitch altogether.

    Fix the plug lead/cap connection first, then retest. If that doesn't do the job, try cleaning the point contacts...a few passes with 600-grit sandpaper followed by a little solvent should do it. If that doesn't do the trick, time to throw a new plug, a set of points and a new condenser at this. The rest of the ignition system is all-or-nothing, i.e it either works or it doesn't. Coils rarely fail and when they do the symptoms are no intermittent.
     
  9. racerx

    racerx Administrator
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    BTW...see that alphanumeric code on the keyswitch (it appears to be H5160 as best I can read it from your photo), give it to Mark at hondakeys.com. He will likely have NOS keys for this lock code.
     
  10. PurplePackFan

    PurplePackFan New Member

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    The wiring harness goes into the headlight bucket so you will need to remove headlight and disconnect pigtails inside bucket in order to pull harness back enough to get key switch disconnected.
     
  11. RDRider

    RDRider New Member

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    Wow. Awesome feedback!
    I'll have a lot to check out.
    Thank you!
     
  12. racerx

    racerx Administrator
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    That's different from my experience. The keyswitch plug sits rearward of the access holes in the frame. You may want to remove the gas tank for access, i.e. you can then reach inside the frame to separate the connector halves...which can be stubborn. But, you should be able to leave the HL end of the wire harness in place.
     
  13. PurplePackFan

    PurplePackFan New Member

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    Racerx you are correct! I was just thinking that he may need to pull it back some to get a good grip on the connector to get it apart.

    I appreciate the help I've gotten from you, OLD CT, Kirrby and others on this forum in the past and I know you guys have been doing this a lot longer than me. Keep up the great work and solid advice!
     
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  14. RDRider

    RDRider New Member

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    This is exactly my issue. I can't reach the connector.
     
  15. racerx

    racerx Administrator
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    Remove the tank, then you'll be able to reach inside the frame, with one hand...up to the steering head tube, if your hands aren't huge. Use a pair of long, 90-degree, needlenose pliers to hold one half of the connector (via the large hole in the RH side of the frame) then you'll be able to use your free hand to pull the other end apart.
     
  16. OLD CT

    OLD CT Well-Known Member

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    There are a couple of metal ''bendable tabs''' that run along the inside of the frame to hold the harness. Run your hand inside and bend out and remove the harness out of them and that will give you some slack. Once the key switch is unplugged, check for spark. You will just have to choke it to shut it off till you buy the key on ebay.
     
  17. RDRider

    RDRider New Member

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    IT'S ALIVE!! ...but man does it need a lot of work. Total Appalachian American start-up method (I'm 2 generations removed from the WV hills BTW). Spark plug wire was so tore-up that by the time I got back to good wire, it was too short! Shot some brake cleaner in the spark plug hole because one of the bolts on the intake runner to the head is stripped and made a make shift plug wire extension. 2 kicks and it purred. Mechanically sounds good so far. Check it out! 20200323_205546.jpg
    Can this wire be spliced, or should I just by a whole new coil assembly? If it can be spliced, any recommendations?
     
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  18. OLD CT

    OLD CT Well-Known Member

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    The wire can be spliced with a kit but a new aftermarket coil costs around 20 bucks. You will have to at least lower/tilt down the engine to get access to the coil.

    Ebay item# 311196846125 $11.89 to your door.
    OR Northeast Vintage Cycles will have a good aftermarket coil. Even ebay has a good coil for $15.89 shipped. Just make sure it physically looks like the 6v coil that is in the bike. There are a lot of cheap junk 12v coils that people try to sell on ebay listed as a ct70 coil that do not look anything like the original.
     
    #17 OLD CT, Mar 23, 2020
    Last edited: Mar 23, 2020

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