kz750 not firing

Patton wrote: The FSM is misleading when saying that one non-sparking plug results in both plugs not sparking.

One plug in the secondary loop may indeed fire alone, provided the secondary loop isn't broken.
For instance a non-firing plug may have a carbon-filled gap allowing voltage to pass through.
Or a plug wire may be shorting to the engine head in a manner whereby the secondary loop is completed.



Good Fortune!

The secondary loop WAS broken when I pulled the cap off of #4 and #1 continued to fire. Maybe the factory coils will kill both when the loop is broken, the Dynas don't. My ignition system is all Dyna, coils, ignition and wires, new 1 year ago and new NGK resister caps. The wires are routed very short and don't touch the frame or engine from coil to cap. There is no random cross firing or shorting. The system has worked flawlessly until #4 plug fouled, due, I think to a leaking choke plunger and that's not a fault of the ignition system.

It's not counter-intuitive. The way the coil is wired with the plugs, it makes lots of sense that the two plugs polarity is opposite. It is a DC circuit after all.

I'm afraid we hi-jacked the thread. Did Arnold fix his bike yet?

TomW wrote: ...The secondary loop WAS broken when I pulled the cap off of #4 and #1 continued to fire. Maybe the factory coils will kill both when the loop is broken, the Dynas don't. My ignition system is all Dyna, coils, ignition and wires, new 1 year ago and new NGK resister caps. The wires are routed very short and don't touch the frame or engine from coil to cap. There is no random cross firing or shorting. The system has worked flawlessly until #4 plug fouled, due, I think to a leaking choke plunger and that's not a fault of the ignition system....

Dyna plug wires usually come with integrated non-resistor caps already built in.
Installation of new resistor NGK caps would entail cutting off the Dyna caps to attach the NGK caps.
If the Dyna plug wires are solid core (i.e., not suppression type), the resistor caps should perform all right, provided they afford the correct resistance, and that "R" designation (resistor) spark plugs aren't also installed.

If not already done, would test run with the fuel tank removed to confirm that there's no high intensity leakage from #4 plug wire to the chassis or engine. The plug wires from Dyna coils are supposed to run up and toward the front before looping down to the plugs. The wires may readily contact the frame and/or the fuel tank, especially with the tank is installed in its normal position.

Has weak spark been ruled out as the reason #4 plug fouled?
If not already done, would observe spark quality on a brand new non-resistor plug (NGKB8ES) to check for healthy fat blue sparks

Would also measure voltage being received at the ignition coil primary winding terminal, and compare it with the voltage measured between the battery posts. The two measurements should ideally be the same.
Also, the battery voltage measured between the posts should be 12+ volts when the engine isn't running, 12~13 volts at idle rpm, and 13~14 volts at 3000~4000 rpm.

Good Fortune!

Would also double-check that the screw head at the Dyna coil primary terminal isn't shorting against the coil mounting spacer.

Good Fortune!

The #4 plug wire may be readily removed from where it's press-fitted into the Dyna coil.

If #4 plug wire is removed from the coil and detached from the plug (and placed on the work bench) so that there's no possible connection between the coil and #4 plug, the #1 plug remaining attached to the coil won't spark, regardless of the coil brand, because the secondary loop under such circumstances is truly broken.
If the #1 plug then keeps on sparking, it's time to call Guinness.

Good Fortune!

Patton wrote:

TomW wrote: ...The secondary loop WAS broken when I pulled the cap off of #4 and #1 continued to fire. Maybe the factory coils will kill both when the loop is broken, the Dynas don't. My ignition system is all Dyna, coils, ignition and wires, new 1 year ago and new NGK resister caps. The wires are routed very short and don't touch the frame or engine from coil to cap. There is no random cross firing or shorting. The system has worked flawlessly until #4 plug fouled, due, I think to a leaking choke plunger and that's not a fault of the ignition system....

Dyna plug wires usually come with integrated non-resistor caps already built in.
Installation of new resistor NGK caps would entail cutting off the Dyna caps to attach the NGK caps.
If the Dyna plug wires are solid core (i.e., not suppression type), the resistor caps should perform all right, provided they afford the correct resistance, and that "R" designation (resistor) spark plugs aren't also installed.

If not already done, would test run with the fuel tank removed to confirm that there's no high intensity leakage from #4 plug wire to the chassis or engine. The plug wires from Dyna coils are supposed to run up and toward the front before looping down to the plugs. The wires may readily contact the frame and/or the fuel tank, especially with the tank is installed in its normal position.

Has weak spark been ruled out as the reason #4 plug fouled?
If not already done, would observe spark quality on a brand new non-resistor plug (NGKB8ES) to check for healthy fat blue sparks

Would also measure voltage being received at the ignition coil primary winding terminal, and compare it with the voltage measured between the battery posts. The two measurements should ideally be the same.
Also, the battery voltage measured between the posts should be 12+ volts when the engine isn't running, 12~13 volts at idle rpm, and 13~14 volts at 3000~4000 rpm.

Good Fortune!

I got the solid Dyna wires, uncrimped the terminals and saved them and the plain caps for another day. 5k ohm NGK caps. Dyna coils are mounted with the towers down and facing to the rear. This puts the secondary connections right over the cam cover and the primary connections at the rear of the coils and using the far mounting hole on the coil core gives me oodles of clearance for the primary connections. Those connections are also very short, going directly to the relay. There, I said it. :ohmy: I continue to use the WG coil mod after all the discussion here. We'll leave that for another day. I'll double check all voltages, and connections. I'll remove the tank and the #4 wire and perform the tests suggested, all to prove that #1 won't die if #4 does. But not today, I have other work to do. I need to paint the tank at least on the KZ1000 but not until I have my remodeling done and my Voyager on the road. I can't be without a rideable bike for more than a day, and only if it's raining. If I prove myself wrong, I'll buy you a Guinness the next time I'm in your neighborhood, where ever that is. When all is tested and I prove I'm right, I'll start a new thread titled Dyna coils rock!

Patton wrote: The #4 plug wire may be readily removed from where it's press-fitted into the Dyna coil.

If #4 plug wire is removed from the coil and detached from the plug (and placed on the work bench) so that there's no possible connection between the coil and #4 plug, the #1 plug remaining attached to the coil won't spark, regardless of the coil brand, because the secondary loop under such circumstances is truly broken.


Have you ever done this? Do you know this through empirical testing, or is this a theory, yet unproven?

Problem solved !!

I love you Steell...you were spot on. Changed the plugs and she fires right up

I would never figured that one out...especially when 3 out of 4 plugs were bad. I mean..what are the chanses of that when she ran good the day before. The plus were less than a year old and have not run more than a couple of hours.

Would have spent weeks on this if I haven´t got info from you. Thanx !

If in doubt, replace the sparkplugs. I've new NGK's fail right out of the box. If you really must use NGK's, try to get the ones made in Japan, it seems the U.S. made ones, are having a quality problem.