CDI Fail?

Discussion in '2-Stroke Engines' started by Timbone, Aug 21, 2015.

  1. Timbone

    Timbone Active Member

    Was returning from the grocery a few evenings ago. I had a nice cruise going then... nothing. Engine stopped firing and I had to coast to a stop and off the road. Luckily I was only about 1/2 mile away. I checked all my electrical connections - they all looked good - and I pedalled home.

    So I'm thinking a carby issue - maybe the jet is clogged? Had fuel in the float bowl. All fuel lines intact and flowing freely. I even put in a new, smaller jet to help lean things out at WOT.

    Put the carby back together and went to ride. No go. Maybe 3 or 4 pops. But mostly just getting cold puffs of air out of the exhaust.

    Pulled the spark plug, an NGK, which looks pretty damn good even after thousands of miles. Pedalled the bike and touched the plug to the cylinder fins and all I could see was weak, very sporadic sparking, when there was spark. Tried the same thing with a new NGK spark plug, and the same thing. I tried to shock myself with the system (it should jolt the bugeezus out of me!) but I could feel some electric but not much.

    Tried again, last night in the dark, same thing. Got a surge of spark at the end of my test and that was all.

    I am wondering if you can fry the CDI by using this spark test method?

    By the way, I have ordered a new CDI and a NGK plug wire.



  2. jaguar

    jaguar Well-Known Member

    you should of ordered a stator coil
  3. crassius

    crassius Well-Known Member

    never hurts to have a spare CDI on the shelf, even if only to rule out the CDI as a problem
  4. Timbone

    Timbone Active Member

    I guess my main question is this: can you burn out a CDI buy doing a spark check (pedalling fast and holding the spark against the case of the cylinder?

    Oh, that CDI needs replacement. it is the original kit one I've used on two bikes. The plug wire has gone past its design life. My guess is the problem is the plug wire so it's a necessary thing.

    Also, I have inspected the stator coil and it looks pristine in there. All the connections look good and the magnet is spinning as it should. If the coil is bad, I have another on hand.

    Thanks, Guys!
  5. jaguar

    jaguar Well-Known Member

    theoretically if the high voltage coil is producing high voltage with no where for the electrical charge to go (if you don't keep the spark plug contacting the head) then the voltage can get so high that it arcs across its own coils and damages the coil. (sparking voltage is around 5500 volts but if there is no conduction path then the coil voltage can reach 15,000 or more)
    so be sure to keep the plug pressed tightly against the head when doing this test. if you do so then there is no risk of damage.
    Last edited: Aug 23, 2015
  6. Does the stator have a white wire?

    If so look very closely for a ground wire soldered onto the housing.

    It should be soldered, and not burnt looking.
  7. I can not post picture yet, but I just had a similar issue, and it was an easy fix!
  8. Timbone

    Timbone Active Member

    The stator has a white wire soldered to the coil. Isn't that the run out to the unused white wire? It looks OK, certainly not fried. (Electronics is my weak area!)

    I may have friend the coil as I did not hold the plug uniformly against the engine case. I had no idea I could fry anything by simply pedaling.

    I appreciate your help, guys. I don't have a good grasp of these electronics.