Volt Readings to the Battery...

I have a '75 KZ 900 Z1 that I have had nothing but
trouble with. I have replaced the voltage regulator,
rectifier, battery, coils, condensers and points. The
problem is that the bike will run just fine for a
short while and then it will lose two cylinders and
only run on two. I'm not 100% sure of the following
finding but when this happens, it seems that if I
hook a volt meter on the battery posts the reading
will jump all over the place. It starts out at 12.2-
12.6 volts, with the bike off. When I start the bike
the reading goes to like 13.4 then to like 14.5 and
bounces back and forth, just as it should. Then all
of the sudden the reading will bounce all over the
place, like 14 to 12 to 19 to 15 then clear to 125, this is when the bike seems to start running like
crap. Now mind you it doesn't miss and pop, it sounds
like two cylinders ran out of fuel and are dead. It
was blowing the main fuse when this happened but it
hasn't done that for a while, plus when it acts up I
don't let it run for very long because I don't want
anything to melt. If this was my bike I would have
already used the sledge-o-matic on it.
Any one have any ideas.

Have you run any test with a multimeter on the stator while it is isolated and did you replace the voltage reulator with a new one and was it a universal fit, it just really sounds like a regulator problem, if the voltage is getting that high it could have spelled the demise of alot of your other electrical components. trace all the wires down to the stator and look for any melted wires. I have seen bad reulators out of the box

The bike had a new and "modern" regulator on it when
my dad bought it but I don't think it was wired up right. I just replaced it with a OEM reg. that was a
used unit but I suppose it could be bad, but to have
two different units doing the same thing, I guess I
have seen stranger things myself. As far as the stator,
I metered the three wires for continuity, I have
continuity between all three wires in any configuration,
but none between any of the wires and the engine cases
or frame. I don't believe there is a short in the wires
or stator.
Does anyone know of an online wireing diagram for the
aftermarket regulator that replaces the rectifier also,
this is what was on it when it was bought but it did
the same thing.

There are a couple of things you can do. Your regulator isn't working as it should. The voltage should be 12 VDC at idle and 14 VDC at 4K rpm. The voltage shouldn't bounce.

The checks you did on the stator said you had good windings but didn't check the magnet. You can pull off the BLUE plug and check AC voltages between the three pins that connect to the stator wires. You should likely check the voltage in every possible combination. The voltages should be pretty consistent from pair to pair and I think all of them should be about 50 VAC but check a manual for the exact value as my memory isn't good. I don't think your stator is the problem nor the magnets.

The regulator seems to be the problem since the voltage varies. The way the regulator works is that it puts out voltage based on feedback from a switched VDC source. In this case, the switched source is the BROWN wire connection. The brown wire feeds the horn and turn signals in addition to this use. First check the wiring and connections leading to the brown connector which connects to the stator. You may even want to try another hot wire that is coming off the ignition switch. Jump a wire from the RED wire connector which feeds your running lamp in your tail light. This is a more direct connection off your ignition switch. See if the voltage jumps around as described in this test. If it doesn't it tells you that the wiring in the brown ciruit has a problem... loose wire, dirty connection, etc...

If the problem continues, then check and clean the other regulator connections... make sure the WHITE or WHITE/RED wire coming off the regulator that tees with the WHITE or WHITE/RED wire off the rectifier bridge is connected solidly and clean and use dielectic grease on the connections as they go to the battery and main fuse. If this connection is bad, your voltage might jump around.

Last, if these things don't fix the problem, replace the rectifier. Those old rectifiers get warm when they are in use and are buried out of the airflow so tend to warm over and over and eventually fail due to heat.

If you have an aftermarket reg/rec, this thing may work a tad differently. There will be three wires for stator connection, a ground and possibly only one other wire which connects to the battery/main fuse (tee). This wire has the ability to carry voltage OUT but also provides the circuit sensing voltage feedback feature the brown wire did on the old style... If you provide the wire colors coming off the "new" reg/rec, we might be able to guess their function.

The way the voltage bounces, it sounds like it could be a loose connection somewhere too.

If you've never cleaned your connectors, I would suggest starting there. I recently had a rash of blown main fuses. I never really found the cause, but I cleaned all the connectors I could find, applied dielectric grease to all the connections, and replaced the fuse box with a blade type fuse block, and this has fixed and/or improved several things.

OK, I will check these things and also, the five
wires coming out of the new style regulator are
as follows,
yellow, red, yellow, black, yellow

I would imagine that the red is for keyed "hot" and
the black is a "ground". Where do the yellow wires
go and what happens to the original rectifier wiring?

Hey everyone, I am not going to hold my breath
just yet, but I didn't like the spot the where
the regulator was grounded so I changed it and
looked for loose connections. After changing the
ground, I started the bike and metered the posts
on the battery, I had 12.5 volts at idle and
14.5 volts at 4000 rpm. The reason I'm not going
to trust it yet is that a couple of times it got
up to 16.5/16.6 volts at 4000 rpm.
The dead cylinders turned out to be just one this
time, #4, and the plug was dead, there was spark
through a tester and a new plug but no spark out
of that plug. I changed that plug and it runs
fine so I'll try it again tomorrow and see what
happens.

The hot wire on your modern reg/rec (it isn't just a regulator I think but a regulator / rectifier) will go to your battery and main fuse. The black should be ground. The three yellow wires will connect to the three stator wires. Shouldn't make any difference which wire goes to which yellow wire. I think the wires on your KZ900 are all yellow coming off the stator anyway. You will also find wires coming from your neutral indicator and oil pressure sending unit in the same bundle.

So if I'm understanding you right, I will,
1) unplug the OEM rectifier
2) unplug the OEM regulator
3) unplug the yellow OEM stator wires and splice
them to the yellow wires on the new unit
4) plug the red wire of the new unit to the
battery and or the main fuse
5) ground the black wire of the new unit

Do the items above that were unplugged just hang
there now, doesn't the empty slots mess up the OEM
wiring by leaving open circuits?