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Power to coil but not spark plugs

Dmatthews

CB750 New member
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Just bought a 1979 CB 750 F. New battery turns engine over. I tested power to the coils, each coil has power. I have no spark at any of the four plugs. I have looked at the wiring diagram, but not sure what would cause zero spark. Thanks to anyone for some help. I have over 20 early Honda scrambler’s, which are much easier to diagnose.
Thanks, Don
 
Hi there,
I assume you get +12v on the black wires when the ignition is on? If so, that's a start but to get "power to the coil" the other wires (blue and yellow) supply a ground pulse signal via the spark units which are triggered by the pickup mechanism each time the crank spins (similar to points). I'd check with a test light or multimeter that the pickups are working. Also check that primary and secondary resistance of the coils, I think the manual has the expected values but the main thing is that the resistances are not open circuit or shorted to ground.
 
New (to owner) bike, may not even have the spark units..........sold to somebody else. They bolt down over the top of battery.
 
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