Voltage Drop With Dyna S

I am finishing up a restoration of a 76 KZ900. It is pretty much back together but the carbs, so it is not running. I was static timing the Dyna S ignition today. I am powering the Dyna with the same red and orange wire used to power the coils. I get 12+ volts at the duplex female connection to the coils (almost same measured across the battery). I plug in the Dyna S and recheck the voltage to the coils at the same point and current drops by about 1.75 volts. Disconnect the Dyna S power lead and the voltage returns to 12+. The Dyna S appears to be working as it triggers the coils when it is supposed to.

Is it typical for the Dyna S unit to cause a drop in the voltage that much? Is the drop because when the Dyna S is powered it energizing the coils or does that happen only when the unit triggers the coil? Thanks!

Follow the circuit from the battery up the harness, through your switches, and check each looking where the drop is. It might have a bit in a few places, possibly the fuse panel. But your harness is losing the voltage do to resistance/ poor connection. You can probably feel the heat with your hand.
There will be a wiring diagram for your bike in "File Base" upper right corner of the KZR toolbar.

pig9r wrote: I am finishing up a restoration of a 76 KZ900. It is pretty much back together but the carbs, so it is not running. I was static timing the Dyna S ignition today. I am powering the Dyna with the same red and orange wire used to power the coils. I get 12+ volts at the duplex female connection to the coils (almost same measured across the battery). I plug in the Dyna S and recheck the voltage to the coils at the same point and current drops by about 1.75 volts. Disconnect the Dyna S power lead and the voltage returns to 12+. The Dyna S appears to be working as it triggers the coils when it is supposed to.

Is it typical for the Dyna S unit to cause a drop in the voltage that much? Is the drop because when the Dyna S is powered it energizing the coils or does that happen only when the unit triggers the coil? Thanks!

Dyna-S modules ground and unground the coils, same as points.
But -- unlike points -- the Dyna-S requires battery voltage to function.

With a good, fully charged battery, and no wiring issues, providing battery voltage to the Dyna-S should not reduce voltage being furnished to the coils.

For testing purposes, could try connecting the red wire from Dyna-S directly to the positive battery post, to see whether the same voltage drop occurs at the coils.

Good Fortune!

If when doing a bypass of the power circuit, there is still drop, then I would suspect the ground. It takes both to complete the circuit, good ground and voltage supply lines.

The original ignition powers up one coil at a time. The Dyna S powers both coils most of the time. So this means there more current than the original system had.

With the original, or Dyna S ignition, anytime the coils are conducting, there will be voltage drops. It's just a matter of how much. You can minimize the drops by cleaning the switch contacts and fuse holders (as MotorHead said). Check the fuse holders, they are usually the main culprit. After that it's usually the key switch and kill switch.

(Just for others who may read this...A factory electronic ignition does not power up the coil until the crank is turning, so a static voltage test can't be done. The bike must be running.)

Update: I powered the Dyna S directly from the battery (thanks for the suggestion Patton). When it is powered the voltage still drops at the coils. Today the battery was just over 13 volts across the terminals. The coil's feed was at just under 11 volts with the Dyna S powered on. When it is not powered, voltage is just a few tenths lower than what I am at the battery. For that reason I think I am good through the wiring harness (new repo) and the ignition switch and kill switch (which were gone through as part of the restoration).

Just to be clear, it doesn't matter which terminals the trigger wires or power supply wires are connected to on the green Dyna coils correct? The coils are connected to the spark plugs and they are in the head so they should be grounding good. The battery is a new AGM gel from Bikemaster. (BTW they are on sale through Ebay and fit the KZ900 perfectly Click here )

Anyone taken any similar readings with a voltage meter and get similar results? Guess I could call Dyna and see if this is typical for that much of a drop when the coils are energizing?

And thanks for everyone's help.

Sounds like a bad ground, check your harness black/ yellow connections. Also the - battery cable to rear of motor, if the electric starter motor works correctly then this battery ground should be OK. More the black/ yellow harness ground.

Powering the Dyna S from the battery directly or not, will not affect the voltage at the coils if the coils still get their power the original way.

The Dyna S, itself, does not use much power. However, the Dyna S is the switch that turns the coils on and off. It is the coils that use the power and draw the current through what is known as the "primary" circuit. So the path of concern, for current and voltage drops, is from the battery to the fuse panel to the ignition switch to the kill switch then to the coils. From the coils, there are separate wires going to the Dyna S, which then is itself grounded to the engine. Those entire paths are the primary circuits.

That is the entirety of the current path that you need to check. Changing the power for the Dyna unit, alone, won't affect the path for the coils, and it's the coil's path that you are concerned with.

Incidently, the spark plugs path to the engine is not at all related to that primary path, so is not a concern for voltage drops at the coil.

Also, to be sure we are on teh same page, all voltage readings should be taken with the black meter lead directly on the batery's negative post. This way, a bad ground won't alter readings.

All of my grounds test good. I use the negative terminal to ground my meter. The starter works. In fact everything is working well.

I emailed Dynatek this morning. They said the Dyna S does not have any dwell control so the coils stay energized anytime the dyna s unit is powered on, drawing 4 to 5 amps. So a drop of 1 to 2 volts is to be expected.

I can't find where anyone has posted any voltage readings at the same point in any related threads. When I get my carbs back from wiredgeorge I'll have a better idea how it runs! Thanks.

If your wiring is up to it, it should carry the amperage Without Voltage drop. Your Headlight would be a similar amperage. If it also had a 2v drop, the light would be dim. I still think you have a wiring issue, or the Dyna unit where it supplies the ground to charge the coils can't handle it. This I would be surprised to be the case but there has to be a reason for the drop. Somewhere there is a connection or wire that is limiting the current.
What gauge wire did you use for the Bypass test, battery to coil primary + ?