1981 CT70 No Spark

Discussion in 'General' started by Patsfan, Dec 14, 2018.

  1. Patsfan

    Patsfan New Member

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    I have a 1981 CT 70 that has no spark. This was running 5 years ago prior to me deciding to break it down and refurb. It is now back together but no spark. I did not do any engine work to it. Thinking maybe mess of wiring behind headlight might be incorrect. Can not find a wiring diagram that matches my 4-wire ignition key switch. Ignition coil ohms out correct. Should there be 6v at the coil when key is turned on? How do I know what K model mine is? Very confused!!!
     
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  3. hrc200x

    hrc200x Active Member

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    81s didnt have a k designation. I dont think you have 6 volts to the coil till you kick it. Is the battery hooked up or the black wires at the battery connector jumpered? Points adjusted to .012-.016 when the t is lined up on the flywheel?
     
  4. OLD CT

    OLD CT Well-Known Member

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    JH2 model. When you buy parts it says 81 CT70A on Babbit's Honda online. There is only one model, ''3 speed auto'' so there shouldn't be any confusion buying wrong parts as the 81 wasn't available in a 4 speed manual.
     
  5. racerx

    racerx Administrator
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    Quick way to either verify or eliminate the wire harness as the problem...unplug the stator output from the modular plug on the harness, then run a jumper from the primary ignition coil to the HT coil. If you get spark, the problem is somewhere in the harness. Be forewarned that if you start the engine you won't have a kill switch function to shut it down and would have to pull the jumper. OTOH, if nothing changes, then it's time to look elsewhere...point gap/cleanliness, condenser, HT coil ground, wiring.
     
  6. Patsfan

    Patsfan New Member

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    Thanks for the replies. I found the correct wiring diagram and verified wiring was OK. Found a problem with the condenser. Corrected that and now have spark!!! Running but not well yet. Engine wants t run at full throttle. On to the throttle cable and carb.
     
  7. racerx

    racerx Administrator
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    Pull the throttle slide, verify that the large notch aligns with the idle stop screw and the thin, top-to-bottom, groove is on the opposite side of the carb opening, where the nylon plastic pin lives. At some point, virtually every CT70 owner installs the slide 180-degrees out, a.k.a. "backward" if you prefer. When that happens, the slide "bottoms out" at a point roughly equal to 1/4 throttle...which can result in the telltale 8000rpm idle.
     
  8. Patsfan

    Patsfan New Member

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    Verified slide is in correct
    Veriied the slide is in correct but I don’t think cable is pulling and retracting correctly. Tried several cable adjustments via nuts on throttle cable but still running all out. Can I remove throttle grip from handle bar and just work throttle cable with pliers?
     
  9. racerx

    racerx Administrator
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    First, unscrew the cap from the carb. Then, with the cap & slide exposed, work the throttle. You should see at least 18mm of total travel. Any less than that means that the cable has, somehow, become "too short"...probably just unseated at one end. There's a threaded adjusting barrel at the carb end, hidden by a rubber boot. If the end of the outer cable sheathing has popped-out, it would be hidden by the rubber boot.

    I am assuming that any binding, caused by the cable or/and twist grip throttle assembly having developed arthritis, would be pretty obvious. With the carb cap & slide still on the end of the cable, but being held in your free hand, throttle action should be light & silky-smooth.
     
  10. Patsfan

    Patsfan New Member

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    Thanks for that awesome info...I will give that a try tomorrow.
     

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