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TOPIC: No Spark after carb rebuild DT400

No Spark after carb rebuild DT400 11 Oct 2018 17:54 #1

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Hello Everyone! I am new to the forum and bought a '75 DT400 a few months back. It started running rough after a few rides and now that it is getting colder I started the process of refreshing it.

My first task was to rebuild the carb. The rebuild went smoothly and after reinstalling the carb, I could not get it to fire. I pulled the plug and it didn't look too bad. I cleaned it and still no spark. I am chacking while resting the plug against the head, but I wasn't sure if that was enough so ran some copper ground wire around the plug and down to the footpeg. Still nothing.

The coil wire has some wear on it, but nothing major that would cause no spark. I cut the wire back a bit for fresh connection and reinstalled the cap. Still nothing. I have ordered a new coil with wire and cap.

I replaced the plug. Still no spark.

I removed the kill switch from the bars. Still no spark.

The bike has no battery but didn't have one when it ran.

I came on here looking for a thread about where to start chasing no spark but haven't found a thread that is definitive or fully applicable to my situation. I also downloaded the FSM and didn't find much for this in there. Can anyone help me out or point me to an existing thread with detailed info?

Here are my questions.

-I want to measure the output of the coil wire. What are the acceptable numbers?

-what is the easiest way to disconnect the kill switch?

-What do I check next?


I will be building up this bike as the fall progresses, but want to make sure it runs right before diving into the build.

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No Spark after carb rebuild DT400 11 Oct 2018 17:58 #2

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Here are some photos of the bike from this summer.
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No Spark after carb rebuild DT400 11 Oct 2018 18:19 #3

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More photos for y'all
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No Spark after carb rebuild DT400 12 Oct 2018 08:58 #4

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Bump>

Anyone have any ideas here? Any thread I should read on the subject?

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No Spark after carb rebuild DT400 12 Oct 2018 17:14 #5

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Based on the title, cleaning the carb is not related to spark loss UNLESS you somehow unplugged a needed wire while wrestling the carb out. Carefully check the stator to harness connection, make sure the kill switch is not shorting (unplug) and unplug the ignition connection.

Sounds like one of those things is interfering.

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No Good Story ever started with a Salad . . .

No Spark after carb rebuild DT400 13 Oct 2018 15:51 #6

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while removing the carb & taking the slide out has the throttle cable up under the tank pulled a wire off heading to the coil. Coil wire is probably orange but wire going into it might not be orange, can't remember, but from the cdi box it should be obvious by process of elimination.
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No Spark after carb rebuild DT400 14 Oct 2018 08:14 #7

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Makotosun wrote: Based on the title, cleaning the carb is not related to spark loss UNLESS you somehow unplugged a needed wire while wrestling the carb out. Carefully check the stator to harness connection, make sure the kill switch is not shorting (unplug) and unplug the ignition connection.

Sounds like one of those things is interfering.



I’ll check these things today thanks!

Can you point me to the places where I can easily disconnect the ignition and kill switch? Looks like they run into the back of the headlight?

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No Spark after carb rebuild DT400 14 Oct 2018 08:17 #8

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RT325 wrote: while removing the carb & taking the slide out has the throttle cable up under the tank pulled a wire off heading to the coil. Coil wire is probably orange but wire going into it might not be orange, can't remember, but from the cdi box it should be obvious by process of elimination.


Thanks for this! I’ll try this today.
Do you know where I could find a good diagram of the wiring?

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No Spark after carb rebuild DT400 14 Oct 2018 08:50 #9

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The service manual which you can download in our tech library. I think there is a colorized version of the diagram in the wiring diagram section as well.

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No Good Story ever started with a Salad . . .

No Spark after carb rebuild DT400 14 Oct 2018 09:16 #10

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Makotosun wrote: The service manual which you can download in our tech library. I think there is a colorized version of the diagram in the wiring diagram section as well.


Got it thank you! I've printed out the pages and will be working on the bike today.

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