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jakewojo 09-24-2012 02:07 PM

1978 DT400 spark issues
Just curious if anyone knows how to test a DT400 CDI. I was just finishing up a long over due project and noticed that the lights were all burnt out on my dt. I have a new battery and coil in it and still no spark. I have to assume that someone hooked up a 12v charger to the bike before i bought it and smoked the cdi. Anyone have a better idea? :ear

Tim McKittrick 09-24-2012 09:55 PM

There's always something like this........

Then you could even ride at night!

jakewojo 09-25-2012 04:53 AM

Cool looking upgrade but by the looks of it i assume that this is mainly for the older model dt's without the cdi ignition.

jakewojo 09-25-2012 04:56 AM

Does anyone know if it is possible to damage the cdi by hooking up a 12v charger? I guess i can take some solice in the fact that I only paid $150 for the bike!

mudgepondexpress 09-25-2012 10:07 PM

I was going to answer earlier but I cannot say 100%. As far as I know (and I have owned quite a few Yamaha's in the past and even currently, including a 1978 DT175 (CDI) and 1978 DT250 (Points), the ignitions system on these bikes are seperate from the charging/lighting system. They can run with no battery and the ignition switch is just a continuation to ground for the CDI/Points. Putting a charger on the battery will not affect the CDI/Ignition at all and won't affect anything unless you turn on the key with the charger hooked up and running. The CDI's rarely die, but that is rarely...I have witnessed one that took a dump.

The battery acts like a big energy sink, thus if you overcharge it, it disposes of the excess current by way of heat (thus boiling the battery).

Check your grounds, ignition switch, spark plug cap, kill switch, even a bad pickup in the case will end your sparking days. It is a simple system, make sure each component is doing its job.


JeffS77 09-25-2012 10:17 PM

yeah what that guy above me said :lol3

but seariously he sounds correct..the CDI is totally separate from your bettery system..should not be a problem.. I have also seen people bake their old Yamaha CDI's in the oven and bring them back to life :eek1

jakewojo 09-26-2012 04:21 PM

Thanks for the good info. Looks like its time for a more thorough round two of inspection!

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