Motorcycle Repair: 1980 honda cb900 continuously sparks, honda cb900 custom, 1980 honda cb900

Question
My 1980 honda cb900 custom fires continuously as soon as the key and kill switch is turned on without even cranking the engine over. I replaced the ignitor boxes thinking that they may be shorting out but that did not solve the problem. Unplugged the control unit still sparks, unplug the pulse generator it stops sparking.does the pulse generator need replaced or is there a hidden problem?

Answer
Hi Larry,

The older CB900 has two pulser coils which would likely
only cause it to fire on two cylinders
if one pulser was faulty.

The pulse coil usually tests around 530 ohms
and should have no grounds to the engine
when disconnected.

The pulse coil is the trigger signal for
the spark unit to activate the ignition coil.

You could check the pulse coils resistance (ohms)
and maybe the gap on the pulse coil which
is .016"-.027".

I would closely inspect the wires leading to the
pulse coils as a short anywhere could be a problem.
The wires may break near the engine case or rub through.

I suspect either the wiring or the pulse coils at this point.

Later models may use different spark units
and pulse coils as the early ones were
a CDI ignition and later are transistorized.
This might create problems if newer parts
were substituted for old versions.


Good luck!
Wayne S.
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