Should I try a new CDI?

Discussion in '2-Stroke Engines' started by armomk3, Nov 20, 2014.

  1. armomk3

    armomk3 New Member

    Ok, this is driving me nuts. So I had the motor running perfectly. The needle had the c clip 1 towards the rich side (bad idea later). Warmed it up for 10 minutes, I turned it off by pulling the spark plug, i did this many times (I know is bad NOW). so I waited again, it turned on fine, I adjusted the the idle with the screw, idling fine now, sounded great, drove great. then the 2nd time i was warming it up, i saw a lot of smoke coming from the head, pretty sure that was the paint coming off, and some plastic from the spark plug wire melting.. So after the spark plug wire melted, it wouldn't grasp very well to the spark plug. So i left it on there and i turned on the motor after that and it was extremely loose but I still rode it for a bit. Then to turn it off I pulled the spark wire again. So now i was confident that my bike ran fine. So now if i remember correctly I turned off the fuel valve but I don't remember, I'm pretty sure I did. Then I checked the spark plug, it was pretty wet so I knew I was running rich. I waited 3 hours, and tried turning it on and it didn't start. It hasn't started since. I wanted a new spark plug anyway so I bought one. I also ordered a new spark plug wire. So those are on the way. But in the mean time I changed the c clip more towards lean side. Then I checked my float, checked my whole carb it was fine.


    Did I kill my CDI?

  2. crassius

    crassius Well-Known Member

    not sure I understand all you did, but seems strange things to do - I have no idea what shape it's in after all that
  3. KCvale

    KCvale Motorized Bicycle Vendor

    Check the electrical system and see.

    My troubleshooting procedure is simple these days.

    Disconnect the CDI from the Mag.

    Ohm the black magneto wire to a head bolt, it should read a dead short.
    If not, check the ground tab on the magneto.
    The new skyhawk CDI's have no white wire, ground is the lower connector but it has a wire from it to ground.

    Old style mags with a white wire have a tab out of the mag that solders directly to the mag base and they can come loose, just hold it down and re-solder.

    Ohm the magneto from the black and blue wire, 320-380 ohms is ideal, an open or dead short means a bad magneto if the wires are connected.

    Ohm the CDI in the 10K-20K scale.
    Red+ meter probe to CDI black wire.
    Black- meter probe to the spark plug cap.
    You should get about 6.9K ohms.

    If not it could be a bad wire or cap.
    Unscrew the plug wire at the cdi, use pliers or even cut it off and dig the junk out if need be and do the same test above again to the cable screw on the CDI.
    If that works get a new wire and plug cap, if not you have a bad CDI.

    If all of that is good there is only one thing left, the magnet.

    That was indeed the problem with this repair on a new build with a 2014 front page engine kit.

    When you pull the 4 bolts out of the magneto mount it should slam itself against the magnet, I mean to the point where it is hard to even get your first bolt in.
    A weak magnet that lets you move the mag around pretty easily is not strong enough to create a spark which is what this repair had.

    And hey, all you need is any kind of switch between the black and blue wires at the CDI.
    I like having a throttle kill button but I sometimes add a key-switch to the CDI to make it hard to steal.

    I don't dink around when it comes to spark, I remove the stock wiring and run some nice black double insulated 16g wire soldered direct from the magneto to the top of the CDI and then cap it off with a hobby box with or without a keylock switch and use an NGK 5944 (BPR&HIX) Iridium spark plug.


    The best and easiest way to kill a magneto engine is to just short out it's output (black and blue wires) and you can do that with any SPST switch or button.
    Heck, you could run some pretty thin wire from the mag to a switch under you seat for a stealth kill switch as when on the engine simply won't even start.
    It won't keep someone from pedaling away, but they sure won't be able to use engine power to help with the escape ;-}
  4. armomk3

    armomk3 New Member

    Ok, so it's not my CDI, I don't know where to look now. I read so many engine trouble shooting guides and they all say the same thing. I've tried everything that's listed. nothing works. Carb jet is fine. fuel in the bowl. 21 mm for the float. C clip in the slide is in the middle. I start with the choke up. all bolts are tightened. note that I had it running perfectly fine before!! fuel is 16 to 1. fuel valve is open, closed when not running. so next since all of those are fine. I started going to the head. So i saw little bit of fuel getting out of head gasket. its sealed all around except for 1 corner has a very itty bitty slight opening. but a dab of fuel is def on the sides of the gasket. its leaking. is that my problem?
  5. fattirejack

    fattirejack Member

    You didn't mention whether you have the kill switch wired up, If so try disconnecting it. Those stock kill switches have a tendency to stick
  6. armomk3

    armomk3 New Member

    kill switch was never wired up, my plan was to wire that last thing when everything was done.
  7. crassius

    crassius Well-Known Member

    sounds like that head gasket is the problem - if you have acorn nuts on the head, they may be binding so that it won't tighten down properly - either use regular nuts, or break the crown off the acorn nuts, or add some washers under the nuts & re-torque the head
  8. armomk3

    armomk3 New Member

    I'll try that crassius. I'll report back later. In the mean time, if anyone has any other ideas I'm willing to give it a shot because I'm pretty close to giving up if I don't find what's wrong.

    EDIT: So if it is my gasket...what could I have possibly damaged at this point? Can a barely visible line opening by the head gasket really affect an engine turning off and on? I mean I can imagine that it would have lost power, but losing the capability to turn on completely?

    EDIT 2: Also, my gap is set at about .025 on my spark plug. Should I set it to .038 like the paper it came with said? Or does that not affect the fact that it doesn't turn on?
    Last edited: Nov 22, 2014