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I've been working on a 1978 Honda CB400TII and I had it running for a little while before it died and has been starting sometimes and not other times ever since then.

I did a bunch of tests on it today (it decided to run for a couple minutes) and they all seemed to meet the specifications. When it died though I rechecked the spark and they were really really weak, I could barely even see them. I'm going to replace the starter coil on it because I just tested that and it seems to be bad. I cant figure out how to test the CDI but is there anything else along with that I should test?
 

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You could explore the possibility that you have a weak /corroded connection in the wiring harness, or the same thing in the fuse panel. I have a bike that has exactly that problem. When it warms up,the wires get hot and loose their connection. I will dig into it later, because i have other bikes to ride
Not easy to find,because the multimeter still checks out at full voltage,but the fact that the wire is not carrying the amps it should does not show up

In an old bike like yours,sometimes taking apart the wiring connections and applying silicone grease to them will improve their performance. A .17 caliber gun cleaning brush is soft copper and is good for cleaning the female side of the connection.
You could also wire in a temporary bypass connection [fuse the line,please]Right from the battery to the wire that feeds the CDI and see if that helps the problem.
Some bikers have added a relay to the ign that is triggered from the ign. key, and the increased voltage and amperage carrying capacity can really increase performance

http://www.vsource.org/VFR-RVF_files/HondaWireColors.htm

The link is very helpful when tracing your Honda Wires
 

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I have been working on my 1979 CB400T "Hawk II", My experience was that when cranked over the spark was hot but only for a few seconds, then a week blue and then nothing at all. Checked the resistances of the stator, all with in spec. Doug the potting material out of the CDI box and found the SCR that fires the coil to have the metal back cracked away from the body of the SCR. Currently replacing the SCR, 1 Diode and one resistor this weekend, hope it resolves the issue.
 
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