Motorcycle Repair: 1982 cb900, volt pulse, yellow wires

Question
i have a 1982 honda cb900 the two center cyl(2&3) arent firing.carbs are fresh coils check good.NOTE:i am a harley machanic that is trying to help a freind.any help please keith

Answer
Hi Keith,

The CB900 has two ignition or spark subsystems.
This means that cylinders 1/4 and cylinders 2/3
have separate ignition components.

I believe you could try swapping
the spark units under the seat
to see if the problem changes over to
cylinders 1/4. If so, then you know
it is the spark unit at fault.

Another thing to check is the pulse coil
for cylinder 2/3. Under the left side body
cover you should find some connectors.
The pulse coil plug for cylinders 2/3 has two yellow
wires. The ohms should be about 530 between the
two wires. The pulse coil has about a one volt pulse.
The pulse coils themselves are under the left engine cover.

Also the ignition coil should have battery
voltage when the key is on and the same
voltage at the spark unit. I think it is
a black/white wire on both.

It will likely be either a voltage problem,
faulty spark unit or faulty pulse coil.
Also clean the connectors with electronic spray
and check the wiring/grounds etc.

Good luck Keith,
Wayne S.
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