Motorcycle Repair: CB400T Ignition problem (no spark from either plug), honda cb400t, motorcycle service

Question
Dear Falcon,

I have a 1979 Honda cb400t which is not sparking.  I checked both plugs and neither are sparking.

What happened was my bike started stalling while running on the highway (1st ride of the year after long Canadian winter).  At first I thought it could be gas so I switched to the reserve tank while still running.  The bike seemed to respond but about two miles later the bike just totally stalled and I rolled to a safe stop on the side of the highway.  As it turned out I had plenty of gas (I also checked the fuel line to the carb which checked out). When I realized I had enough gas I tried again several times to start but no response.  I then checked the spark plugs and determined neither was sparking.

Based on info from the Clymer manual (includes 400-450 cc twins 1978-1987) it could be the CDI unit or the ignition coils.  The confusing thing about this is on the Rebel 450 there is a CDI unit but for the cb400t - designated all other models in Clymer - there is no apparent CDI unit in the diagram of the ignition system but the wording of the manual would indicate there is one.

Clymer indicates that for my model I should take it to a motorcycle service center because there is no way to test the CDI on my model.  You can test on the Rebel 450 but not for the other models.  Apparently the only way to test the CDI unit for the other models is to do a "remove and replace" to determine if it is the fault.

If the problem is obvious I would rather just purchase the replacement parts and swap them myself.  Is my problem obvious or would it be prudent to take it to a mechanic?  Also, based on how my bike died is it possible for the ignition system to falter like this?  Wouldn't it just die without any warning?

Thanks very much in advance for your advice.

Attila
Toronto, Ontario

Answer
Hi Attila.

Have you checked the ignition coils themselves? How about the ignition circuit?  The coils could be bad or there could be a short in the ignition wiring.
 Even though it could be the CDI unit, they are not known for going bad, but wiring will often go bad as will coils. Particularly on a bike that is 27 years old.

Check the coil in accordance with the bench test proceedures and specs.  If the coils are good, then check the wiring before replacing the CDI.

Good luck and ride safe.
FALCON