Odd spark issue - need help

Discussion in 'Motorized Bicycle Trouble Shooting' started by Chaz, Aug 9, 2017.

  1. Chaz

    Chaz Active Member

    Joined:
    Jun 3, 2012
    Messages:
    910
    Likes Received:
    36
    I have the basic PK80, mildly ported, nt speed carb. Now to the problem. It has been acting up a bit on start up and warm up. It will fire up right away but I need to rev it high to keep from just instantly cutting out. Never seen this issue before. It started happening out of the blue after running fine for a couple of years. One thing to mention is I got a shock from touching the plug wire and or the plug cap. That was through my leather gloves. I'm pretty sure I've touched these before and never had a shock.
    I haven't made any changes and this came out of nowhere so I'm a bit confused.

    Does anyone have any suggestions?
     
  2. Tyler6357

    Tyler6357 Member

    Joined:
    Mar 15, 2012
    Messages:
    803
    Likes Received:
    10
    Sounds like a short in the CDI or the CDI wire. Did you put a new spark plug boot on it when you got it or did it come with a good one? Did you have to take the spark plug cap off to put the boot on the spark plug or not?
     
  3. Chaz

    Chaz Active Member

    Joined:
    Jun 3, 2012
    Messages:
    910
    Likes Received:
    36
    Thanks Tyler, I have an NGK boot but it is the "no cap" type. It has been working fine all this time. The plug wire is not the solid copper type. I'll check over the wiring. The funny thing is after its all warmed up it seems to be fine and idles at fairly low rpm smoothly. I'll do a shock test after a ride and see what happens. I only got zapped when it was still warming up.
     
  4. crassius

    crassius Well-Known Member

    Joined:
    Sep 30, 2012
    Messages:
    3,376
    Likes Received:
    35
    I've seen in cars, that silicone resister wires become leaky over time to the point that some arcing can be seen at night.
     
  5. Chaz

    Chaz Active Member

    Joined:
    Jun 3, 2012
    Messages:
    910
    Likes Received:
    36
    Thanks, crassius, I'll swap out the plug wire, which I think is silicone and carbon, with the stock one. I just hope I can find it. Will report back later.
     
  6. Chaz

    Chaz Active Member

    Joined:
    Jun 3, 2012
    Messages:
    910
    Likes Received:
    36
    I went to swap out the plug wire and found that it is a copper wire core. I must have thought of another engine. Anyway, the problem is still there and goes away after she warms up so I now suspect the magneto. Possibly a break in the winding that closes when it heats up.
     
  7. Tyler6357

    Tyler6357 Member

    Joined:
    Mar 15, 2012
    Messages:
    803
    Likes Received:
    10
    I prefer the kind that you don't have to remove the spark plug cap to connect them. I replace with the other type because they are so cheap ($5 or less) and easy to put on, better for vibration and just makes a better connection. I would do that first just because it's cheap and better.

    Second, put the cap on your spark plug or get a good new spark plug. It could just be time to replace the plug. If you have another one you should test with it. I recommend using NGK: B5HS, B6HS, B7HS, or B8HS.

    Next, test and see if the problem is solved. If the problem is not solved it certainly could be the magneto or the coil and you should do a visual inspection for anything obvious on those. The thing that makes me think it could be the CDI boot is because you said the wire is giving a shock, it shouldn't be giving a shock unless it's got an arc or thin connection or something. Perhaps it goes away once warmed up because the heat makes it briefly connect better but if that is what is happening it will soon fail.
     
    #7 Tyler6357, Aug 10, 2017
    Last edited: Aug 10, 2017
  8. Chaz

    Chaz Active Member

    Joined:
    Jun 3, 2012
    Messages:
    910
    Likes Received:
    36
    Good ideas! Thanks Tyler.
     
  9. lobsterman61

    lobsterman61 New Member

    Joined:
    Aug 6, 2017
    Messages:
    5
    Likes Received:
    0
    Hi Tyler, I have 80 cc for about 2 weeks now, didn't drive it very much and now no spark. It was slowly getting harder to start & now it won 't start-, no fire. I tried 3 different spark plugs and no go, any help would be great, thanks.Leo.
     
  10. Chaz

    Chaz Active Member

    Joined:
    Jun 3, 2012
    Messages:
    910
    Likes Received:
    36
    Leo, Tyler is welcome to respond here but you should start your own thread to keep the info relevant to your bike. You will need to provide more information about your bike. We can assume that you have all stock parts and are still breaking in the engine. What fuel/oil ratio are you using? Did you make any adjustments to the carb? Did you rinse the gas tank before installing? Get a proper spark plug from Tylers list above. What plug gap are you using?

    Just off the top of my pointy head I would suggest you re-torque the head. First check for any oil around the gasket there. If you are using the stock acorn head nuts then replace them or just cut the caps off.

    And here is a great thread to read through that may give you some ideas:
    https://motorbicycling.com/threads/so-your-ht-bicycle-engine-wont-start-well-lets-take-a-look.35090/

    good luck
     
  11. Tyler6357

    Tyler6357 Member

    Joined:
    Mar 15, 2012
    Messages:
    803
    Likes Received:
    10
    Are you certain you are not getting a spark? If you are not getting a spark it is most likely the coil, magneto, or CDI. Check this old thread that explains how to test. https://motorbicycling.com/threads/so-your-ht-bicycle-engine-wont-start-well-lets-take-a-look.35090/
     
  12. Chaz

    Chaz Active Member

    Joined:
    Jun 3, 2012
    Messages:
    910
    Likes Received:
    36
    Well, I know many of you have been waiting for me to solve the greatest mystery of the ages (yeah, right). So I finally got around to swapping out the spark plug. Bang! problem solved. In my defense I've never had a plug fail like that before. I remember noticing that my old falcon was not running quite as smooth as usual and thought it was maybe time to change the plugs. To my surprise the gap was almost completely closed with ash deposits. I couldn't believe that the thing even ran. God I love those straight sixes.

    Anyway, it was just a faulty plug. The electric path was iffy until it warmed up a bit and then it closed and ran fine. Sometimes I overlook the simplest solution.

    Thanks guys for pitching in to help out
     
    Tyler6357 likes this.

Share This Page