Spark v. Starter

I have noticed that if my battery is much less than fully charged the starter will spin the engine at normal speed but it will not start.
I am not talking a flat battery just not fully charged, the starter will spin the engine for 15 seconds a time for repeated efforts= maybe 30 trys fiddling with the choke and checking fuel feed all those things you do when it won't cooperate.without dropping any speed.
The motor is 400 C2 and I have the plugs gapped at 32 thou as per manual=high current pointless electronic transistor ignition fitted.
Is this usual or should I be looking to improve things?

If it's not fairly new I would replace the battery. I suspect the issue is that the amount of power used to turn the engine over doesn't leave enough power to properly fire the plugs. Ed

This is a fairly common problem.
To be sure that the battery is faulty, connect your volt meter to the battery with everything off. Note the reading. Turn the key on, press the start button and note the reading. If you see a reading much below 10v, it is new battery time.

You will first want to identify which ignition you have.

The Kz550H1 used a mechanical advancer for the timing advance. The Zx400C2, used an electronic-advance with no mechanical advancer. The ignition control modules are not interchangeable between the two types.

The control module for the Kz550H model will look like a small box molded from one-piece of cast aluminum with heat sinks. It will have wires coming out of it.
The control module for the Zx400C2 model will look like a slightly larger box made of smooth sheet metal. It will have pins on with a connector directly attached to the box.

As long as the motor is turning over at a relatively normal rate, the early ignition should have no problem producing spark. If there is a problem, I suspect you are losing voltage in the circuit path going to the coils and ignition. The biggest culprit is usually the fuse holders. Next would be the kill switch. Next would be the ignition switch.

Iteresting side note: both manual supplements mention the '85 Zx400C2 and '86 Zx400C3, but there is no mention of an '84 Zx400C1, or any Zx400C1 for that matter. Maybe the Zx400C1 had it's own dedicated manual so was not included in the supplements for Kz/Zx/Zr 550. But the Zx400C2 was rolled into those supplements due to being so similar. Or maybe there was no Zx400C1?

Ed's thinking appears to be on the button.
I will check the ignition module issue as it appears to be a bitsa and as there is no mechanical advance fitted under the pickup plate it is probably 400c2.
It makes sense to do the voltage check now I know what I should be looking for re voltage drop.
Done continuity check on battery/ ignition/ kill switch path and that seems OK but electronic ignition makes extending that path to the coils beyond my skill set.
My pdf of the supplement is not razor sharp and the wiring diagrams are unreadable, given the wiring modifications and his preference for green/white wire a readable copy would be very useful. The supplement does not seem to be listed in the manuals folder in tech.
Thank you all I may be back on this one.
Anent the absence of C1 information I think it may be that it got lost in the series change Kz to Zx as a model that never went into production.

Regardless of type of ignition, the coils and igniter get their positive 12v power from the same path. The red/yellow wire just branches off to the coils and igniter. The positive side of the coils and the igniter's power wire should have battery votlage. They usually produce reliable spark down below 10v.

Since someone would have had to modify the wiring in order to swap the ignition to the newer style, you will want to do a full trace of the ignition wires to make sure the installation was done porperly. A wiring diagram won't be exactly correct if the person had to use extra wiring.


For your information, because it does occasionally become a bug, the Zx wiring has a "safety" circuit which looks for kickstand, neutral, and clutch status to kill the ignition or prevent starting under certain conditions. It is a single wire on the igniter and can be defeated by grounding it. The exact color of the wire depends on which model the ignition came from. Since it was already a modification, and there is no kickstand switch on the 82 Kz550H, he may have already defeated the safety and so you would find two wires from the igniter connected to ground.

That's useful stuff thanks.
A far as the wiring diagram is concerned it would be useful if the component labeling was legible, I am better with magnetos and dynamos than energy regeneration systems and electronics, although I am beginning to study can bus voltage differences as a necessity. I can just about do relays but pcbs are beyond me.
Regarding the safeties and lockouts the kickstand,clutch lever and neutral position all function to inhibit start/clutch release even though I do not have a neutral light, something I intend to correct.
There are no warning lights of any kind in his simplified wiring, presumably if it isn't wired in it won't interfere with anything. Given his standard of wiring, which includes bare wires twisted together without solder under heat shrink x3 so far I agree the less live wires the better.
I am currently ( pun intended) trying to find a power/earth warm point created when the ignition is live as i suspect there is at least one..