Motoplat gone sour.

[Lloyd Boland]

This is probably directed to Dane, but anyone with suggestions is welcome.  Besides my 250 MC-5, I have a 1974 CZ-400 with a motoplat ignition.  The last time I rode it, in practice before a race, it was running great then all of a sudden it just stopped running and made a couple of sound like it was mis-firing.  It didn't seize, just stopped firing.  It wouldn't restart.  There was no spark.  I put it in the trailer and it was too late to work on it when I got home.  The next weekend I pulled it out and it had spark.  I started it up and it sounded ok for about a minute then stopped.  I kicked it over again and it restarted but stopped after only a few seconds.  I couldn't get it to restart.  Pulled the plug and no spark.  I undid and cleaned all the wires, good contacts.  I have a separate wire that runs from the ingition to the coil mount on the frame so I don't have to worry about grounding issues from motor to frame, etc.  Still no spark.  Someone told me they had a similar problem and it was a lower coil problem, and when the motor warms up the coil fails.  I am completely ignorant on electric issues.  I know how the wires run and how to time the bike ( have done it 100s of times), but the workings inside the ignition are like a foreign language.  Is this fatal, are there fixes, or do I just junk it and buy new?  They stopped making motoplats for CZs many years ago but I understand there are some new replacement ignitions.

[tmc3c]

Hi Lloyd,I am sitting here with nothing better to do and I thought I would ask you a question before Dane gives you the answer,and that is the kill switch wire is it hooked up still and not shorting out? I just Had this problem myself and well there is my 2cents.

Thomas Carmichael

[Lloyd Boland]

Thanks Thom.  I disconnected the kill switch also.  No change.  A good thought.

[dkwkid]

I just changed out the Motoplat on my brothers 125cc Six Days.It was missing so we pulled the flywheel-the potting material was cracked at the ignition coil(low end)and goo was coming out. It looked like the coil overheated.I have a few of these older motoplats with cracked and discolored source coils.I too am curious on why these coils get so hot.Usually high current=heat, maybe the internal resistance of the top coil has gone down.Dane, any insight?

[TGTech]

Lloyd,

   First off, despite the fact that you have a ground wire running from the stator to the coil, I always suggest going through the normal ground cleaning procedure. It's just good practice. And that includes removing the seal plate from the engine and cleaning up the screws and everything else from there out. Regarding the ground wire thing: When asked about the grounding thing, Motoplat told me that if you completely isolated the coil from the chassis (and in turn, the stator) you would need at least a 12 gauge wire. So a 16 or 18 gauge wire, wouldn't be large enough to carry a ground, should the mounting grounds fail.

   That having been said, the problem that you detailed, sounds like the  trigger circuit or the coil failing. Obviously, if you have another coil to use as a test mule, give it a try. If not, then at least try and borrow one for enough time to see if it reacts the same way as if your original coil was still in place.

   If it is the trigger circuit failing, it will eventually, completely give up, and you won't be able to start the engine even for the short period of time that you can now.

   As always, you can send the system into the shop, and I'll give it a thorough run on the bench.

   Regarding the cracking thing, that is usually a result of allowing the stator to have some moisture soak into the potting material and then getting the stator hot again. Once the moisture turns to steam, the pressure has to go somewhere, and it usually  causes the potting material to crack.

   The gooey material that "seeps" out of the cracks, is normally the adhesive from the tape that is used to hold the outside few turns of wire on the bobbins prior to the potting process. When the stator gets hot, the adhesive liquifies and seeps out of the crack.

   I hope I've been able to answer your questions. If you need more guidance, give me a call: 440-988-4474.

Dane

[Lloyd Boland]

Thanks Dane. I'll give you a call to get all the information needed to send you the whole system.
Lloyd

[Lloyd Boland]

3 hour time difference, just missed you.  I'll call on Monday.  Thanks again.