77' Kz750BE No spark?

I'm pretty new to this scene, recently acquired this Kz750 as "ready to ride with some tlc" The bike itself is in pretty good shape, other than an absolutely disgusting build up in the tank. To the point, I am getting power from the points to the coils, but not from the coils to the plugs? Yes this is a symptom of bad coils, but they have already been replaced with coils that came out of a already running bike. Is there something I am missing?

Use an Ohm meter to check continuity from the points wire at the coil (which on my 750B4 is a blue wire) down to the points.

Turn the ignition OFF to do ohm tests.

If that is good, check from that wire to ground and you should read high resistance with the points open and zero when they close.


If you have 12V at the hot side of the coil primary and the points are breaking the blue wires continuity to ground, you should get a spark. If not, the coil is dead or the spark plug is fouled.

Clayton! wrote:

I'm pretty new to this scene, recently acquired this Kz750 as "ready to ride with some tlc" The bike itself is in pretty good shape, other than an absolutely disgusting build up in the tank. To the point, I am getting power from the points to the coils, but not from the coils to the plugs? Yes this is a symptom of bad coils, but they have already been replaced with coils that came out of a already running bike. Is there something I am missing?

Even perfectly good coils receiving proper voltage matched with perfectly good spark plugs do not guarantee the desireable fat blue spark.

Often there's a problem in the high voltage secondary loop running through the plug wires and plugs and across the head.

Usually would suspect:
Deteriorated, broken or leaking plug wires;
OR poor connection:
coil > plug wire;
plug wire > cap;
cap > plug;
OR bad plug cap.
Any of these issues may alone prevent a perfectly good coil from firing a perfectly good spark plug.

And would also heed bountyhunter's advice about checking the signals from the points to the coils.

If not already done, and uncertain as to whether coils are good, would also ohm test coil primary windings and secondary windings. (Let us know if more details are needed about ohm testing coils).

Good Luck!

If not already fitted with inline fuel filter(s), would urge putting a new inline fuel filter in each fuel line, to assure no gas reaches the carb without first passing through an inline fuel filter.

Good Luck!

Clayton! wrote:

To the point, I am getting power from the points to the coils, but not from the coils to the plugs?

That's not how they are supposed to be wired. The coil primary side has two connections: the positive side should have a switched 12V line coming from the ignition switch. That wire is usually red or yellow red or something with red in it. If you turn on the key, you should read 12V on it.

The negative side of the coil primary (blue wire) goes to the points and the points connect it to ground when closed and open it when they open up. The spark occurs when the points open.

The spark plugs are connected to the secondary high voltage winding on the coil, which is actually a transformer. On B model coils, the wires are molded into the coil.

Thanks for the information, ohmed everything and found the problem Fired up, ran for a few sec then a realized both of the carbs were leaking like a shiv :ohmy: Any idea on the carb specs for this bike?

Clayton! wrote:

Thanks for the information, ohmed everything and found the problem Fired up, ran for a few sec then a realized both of the carbs were leaking like a shiv :ohmy: Any idea on the carb specs for this bike?

If they are like mine, they are Mikuni BS-38. Rebuild kits are available from Keyster (check loudfastugly.com for them)

www.loudfastugly.com/