1978 KZ650SR poor charging.

Hi, my 78 KZ650SR has poor charge. 12 .7 @ 4000rpm. My 1-phase stator reads 65AC volts @ 4000 rpm. The book says it shuld be 75AC volts. Is 65AC volts that low, or does it sound more like the regulator rectifier unit.

I'd rather the reg/rect unit to be faulty as it would be a cheaper repair.

Any advice? Cheers

First the numbers you posted sound low. As to cause, there could be several different things that can create the low charging voltage. I would suggest you make sure you have a fully charged and healthy battery. All kinds of things can and do happen without a healthy battery. Check all the wiring and connections within the charging system to make sure they are clean and making good connections this includes the ground part of the system.

What you have posted indicates to me you are making use of a service manual for test procedures. But would ask have you done anymore of the tests on the rec/reg , or on the alternator other than total voltage test? If you have what are the results of these tests?

Hi, thanks for the reply.

With the reg rect unit I have done a continuety test between power and each two yellow wires then reversed the multimeter leads and done test again. Seems ok as it had cont one way only.
I then did the black wire and two yellows and had no continuety eithe way with the multimeter leads. Indicates fauty by going off youtube. I cant see the relevence of doing the black (earth) wire .

Hope this makes sence

Ok,

Let's see if we can figure this out.
Get your meter and set it to DC V.

Start the bike
black probe on negative battery terminal( the metal part of the battery not the cable)
red probe on positive battery terminal
Note voltage

raise rpm to 2000
note voltage

raise rpm to 4000
note voltage
Voltage should go up as rpm goes up

Turn on high beams
note voltage
voltage should not drop

allow to idle
move red probe to red/white wire at reg/rec
note voltage
Should be close to the voltage measured at the battery. If lower than .4v compared to battery voltage then you may have too much of a voltage drop on the red/white wire.

move red probe to yellow/black at the reg/rec.
note voltage
This voltage should be less than .5V
any higher then you have too much voltage drop on this ground wire.

The DCV at idle 12.4v.
At 2k is 12.7v
At 4k is 13.1v
No real difference with higj beem on.

Voltage at red and white wire is same as battery.
Voltage at black and yellow wire is nothing shown?

Your battery wiring to your reg/rec seems fine.
Your battery is being charged and maintained by the charging system.
It may be a couple tenths low though.

put your meter on AC V
bike idling
The reg/rec connector for the 2 yellow wires coming from the stator.

put a probe on each of the yellow wires on the reg/rec side of the connector
note voltage
then switch to the other side of the connector and measure the yellow wires on the stator side
note voltage
they should be exactly the same
You are checking for voltage drop across the connector

turn off the bike
meter on Resistance
disconnect the yellow wire connector from the reg/rec
on the stator side of the connector put a probe on each yellow wire and measure the resistance of the stator.
note resistance

take one probe and put it the stator case
note resistance
take the probe on the yellow wire and move it to the other yellow wire
If you see anything less than infinity, your stator is shorting to ground.

I havent checked the resistance but it's producing 65acv at the stator side of the connector.

I'll check resistance on the weekend.

Thanks

Yep,
I saw the 65V reading at the beginning.
The measurements I'm having you do is to find out if you are losing voltage in the wiring and connectors.

There may be a possibility that the magnets in your rotor have lost some of their magnetism as well.
Hopefully, we can narrow down your problem so you aren't throwing parts at it.

Found red wire crushed and cruddy so put new connection on. Black doesnt look too good either.

On tick over same acv on either sidr of connections on reg rec block 13acv .

Some resistence between two yellow wires.

Zero between either wire and and engine case.

Thanks for your help so far. Cheers

Problem solved. I got a new reg rect, done some tests and compared the old and new one. Looked like the readings with the old lack wire were suspect.

Put new one on and now it's working as it sould. A long test ride for me this weekend.

Thanks for the input and advice / help. Cheers

Good Job!
Have fun riding.

Glad to hear you solved the issue!