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TOPIC: 75 dt400 ignition/electrical issue

75 dt400 ignition/electrical issue 12 Aug 2017 15:01 #1

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Ive been slowly (between other projects) chipping away at a 74 dt400. It has 320 miles on it and 100 of them are mine. After tires and a few other maintenance items, it's developed a running problem that's getting worse. It basically shuts off or I should say barely can be kept running in neutral after riding a few miles. I'm familiar with Kawasaki triples cdi systems but I'm not so familiar with this one. Where do I start? Coil? Ignition box? Compression and carb are good. I'm sure it's an age related ignition problem but I'm looking for a good starting point to troubleshoot. Thanks

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75 dt400 ignition/electrical issue 12 Aug 2017 16:56 #2

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Hi grey, start with the cheapest components first, plug/cap, -cut 10mm off H.T lead, ,- then new coil, . also check ALL connections, , then its CDI BOX, [ SWAP] then stator, [ swap,. ]
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75 dt400 ignition/electrical issue 13 Aug 2017 10:09 #3

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You could send it into DEET for testing of the system, and he can give you a diagnosis of the exact cause. If it is the CDI box, I am working with a vendor to develop an aftermarket new replacement. I have a test unit in hand and it works great! Better than my known good stock one. They will hopefully be available soon. Also there are a couple of aftermarket replacements if yours cannot be fixed for a price you are happy with.
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75 dt400 ignition/electrical issue 13 Aug 2017 20:09 #4

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Would have expected 1974 to still be a DT360A but no problem as i think the ignition stator is probably the same for a few years. So if you're sure it's an ignition issue then most likely is the ignition source coil [ign charge coil not to be confused with the lighting/charging coil]. Not easy to diagnose if it starts ok when cold & untill they give up all together it can be a bit of a waiting game. Usualy when they fail they will stop & not keep running at idle, also when starting to fail & stop when hot they just won't kick start till cooled. Jeez i'm talking myself into a corner again!!. A possibility 'is' if it cuts out at revs then chimes in at idle & won't go above is that it's the pulser coil [trigger coil] which [looking at a parts pic] it looks the two stage type my DT360A had. In my case [30 years ago lol] it packed up on the starting half & would only run at above idle. So i swapped around trigger wires to have it start & run on the advance half [second half]. All very well but had to kick it hard or it kicked back & took no prisoners. Ran perfect when started. Video of what it's doing would be good but not easy to do. Might have the resistance measurements here, i'll go look. Need a lie down after all that.
Ok, the nearest i can find here in my 'bible' is an SC500 MX from "74 which had basically the same mag minus lighting coils so the charge coil 'brown to red' says 204 ohms but they were a bastard to start & people would get them rewound to a higher value so a typical resistance would be 350 ohms for this type coil. Pulser coil 'white/red--white/green' is 85 ohms, give or take a bit. Trouble 'is' yours plays up when hot & by the time you test it--it will have cooled a bit. That's enough confusion for this time!! [not outa petrol].
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Last Edit: by RT325.

75 dt400 ignition/electrical issue 14 Aug 2017 04:09 #5

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Thanks for the ideas guys. I'm going to try some tests this week. The trick will be running it but not getting too far when it shuts down. My wife is getting sick of me calling for rides

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75 dt400 ignition/electrical issue 14 Aug 2017 10:45 #6

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My bet is the pulser. I had a 400 with this problem and the pulser fixed the problem and I moved the same bad pulser to 3 different bikes and the same problem followed the pulser. Those pulsers did not react well to getting water and dirt rubbing them by the spinning magnets. I think it breaks the fine wires inside the pulser coil. Clean up the stator and make sure there is clearance between the pulser and the spinning magnets and then seal the cover so dirt and moisture gets in
Doug

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75 dt400 ignition/electrical issue 14 Aug 2017 15:44 #7

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Runs until hot then won't idle, stalls and won't start again until cool??? Yep, that would likely be the pulser (pick-up/trigger) coil on the stator. That's my guess, anyway. Seen it before.
Measure resistance and insulation to ground when cold and again when hot. Should stay the same.

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75 dt400 ignition/electrical issue 15 Aug 2017 05:41 #8

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Yes think those two wire two stage pulsers you measure between the two wires & not to earth like a single wire job. Looking up top i see i said 85 between the two wires [that's from the yamaha book]. but i'm sure when mine packed up that i figured which half was crook probably by going to earth individualy then earthed the crook one. Then again--rethinking, i most likely left say the white/red hooked to the box & earthed the white green from the box seeing that part of pulser was faulty. [Sorry--are ya still awake!!]. Just replace the pulser!! but still might be the Source coil.

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