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CB400A/CM400A/CM450A Hondamatic CDI resistance test from FSM

Maraakate

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For those who have unfortunately read the Clymer manual you will note it purposely omits the CDI test saying it was unreliable and that Honda even disowned the test. This is partially true, but the main reason the test was unreliable is that people were using analog meters back then and those meters were very sensitive to the battery voltage remaining so you'd get a fair amount of false readings.

The following tests assume you have a fresh battery. CDI and meter should be about room temperature or the readings may change a little bit. You will likely have variations in numbers. About 10-20% variation should be OK. If in doubt, ask.

Here is the official FSM test with an Analog Meter. Make sure the scale is zeroed. You will want to use Kohms setting on your meter. Polarity of the probes matter.

CM400A_CDI_AC_Generator_Test.jpg

Here is my test for use with a Digital Meter. You may have to set the "range" manually or you will get strange results. Polarity of the probes matter.

400A_DVM_Test.PNG
 
Last edited:
You've completed one of my projects. I've been meaning to run these test with a digital VOM vs the SP-10D Honda tester to see if the values were the same.
Thank you
 
There is one thing of note about this test that I forgot about. Pay close attention to that table, there is a positive and negative side. In some directions it will read infinity and throw you off and think the CDI is faulty.

I just tested this on four CDIs. One original, one repaired, and two I built.

Here are some typical readings

SmartSelect_20220609-225340_Gallery.jpg

I didn't note the directions, so don't rely on the order being the correct polarity. But this should give you a ballpark of what to expect with a DVM. All readings were in mega-ohms with the exception of green to green/white. That should be somewhere around 80 ohms as it's slightly related to the ground circuit for the sidestand safety. You can actually leave that disconnected if you want to bypass a faulty sidestand switch (or suspect it is faulty).

The book doesn't mention a test for green/black because this is simply a jumper which is for the change relay. It doesn't actually lead to the CDI.
 
Small update to this. I noticed on the CM400T CDI I was working on Black w/ White would only read continuity to Blue. I vaguely remember this being the same quirk on the CM400A. I just went ahead and verified that. So don't be alarmed if B/W isn't reading like the book says.
 
Small update to this. I noticed on the CM400T CDI I was working on Black w/ White would only read continuity to Blue. I vaguely remember this being the same quirk on the CM400A. I just went ahead and verified that. So don't be alarmed if B/W isn't reading like the book says.
This is consistent also with people using the Ignition Diagnosis thread, over 50% get funky readings when testing that circuit of the harness.
 
I've went ahead and tested this correctly with a DVM. You may have to set the "range" manually or you will get strange results. Polarity of the probes matter.

This assumes you have a fresh battery in the DVM and the CDI is disconnected. CDI and meter should be about room temperature or the readings may change a little bit. You will likely have variations in numbers. About 10-20% variation should be OK. If in doubt, ask.

400A_DVM_Test.PNG
 
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