77 KZ750 Twin Stator Diagnosis

Im not as knowledgeable as some about bikes, but I can kind of find my way around.

I have a recently bought 1977 Kawasaki KZ750B and I cant get to the bottom of a problem.

What caused me to check is, the running light part of the 1157 bulb on the brake light, keeps blowing after a while. When I put a multimeter on the battery, it shows the bike is charging fine, but occasionally, just for a split second, drops to 4v, or 10v or 9v and instantaneously comes right back up. I took the bike on a 50 mile journey over the weekend and it was fine though it has the situation i just described.

Today I looked through the manual, took the tank and rear fairing off, and went through every single connection, even in the headlamp. Bike is still doing the same thing.

I also tested the stator, with what little i know, while on the bike. I disconnected it from the brand new regulator, turned my multimeter to 200K ohms and put the postiive lead into one of the stator connector pins and put the negative onto the battery.

2 leads read 1. and the other, 00.6. Is there a problem with the stator?

Like I said, the Deltran Battery Tender LiFePo4 seems to be charging fine.

Thanks guys.

Maybe loudhvx will chime in. How many yellow wires does your stator have? It doesn't sound like the stator was tested correctly. Resistance tests typically are supposed to check the resistance of an isolated component or wire. My 81 KZ650-CSR has a 3-phase stator w 3 yellow wires & for the resistance check you're supposed to put the meter probes on the yellow stator leads, testing pairs of yellow wires, 3 tests total.

ps: kind of like you, I'm not that knowledgeable but can usually find my way around a problem. :blush:
....

martin_csr wrote: Maybe loudhvx will chime in. How many yellow wires does your stator have? It doesn't sound like the stator was tested correctly. Resistance tests typically are supposed to check the resistance of an isolated component or wire. My 81 KZ650-CSR has a 3-phase stator w 3 yellow wires & for the resistance check you're supposed to put the meter probes on the yellow stator leads, testing pairs of yellow wires, 3 tests total.

ps: kind of like you, I'm not that knowledgeable, in some areas anyway, but can usually find my way around a problem. :blush:
....

Thanks so much for responding. My stator has three wires, and they are - 2 yellow and one black and yellow. Im assuming it is in good working order because the battery is being charged perfectly. As I mentioned, the rec/reg is brand new.

2 yellow stator wires = single phase stator. I assume you would test the resistance between the yellow wires. Also, check the AC output of each yellow wire. That's about all I know. I don't know why the voltage is dropping intermittently. maybe shorts in the stator or a wire fault somewhere? but just guessing. Other things to check would be the handlebar controls & the ignition switch >> they have soldered connections that can fail.

....

The 77 750 twin stator should have 3 yellow wires. You will want to look into why one is black/yellow. Maybe someone just replaced a bad yellow wire with a black/yellow one, or maybe the black/yellow one is not related.

Black/yellow is normally ground on all Kz's.
The rectifier and regulator are two separate units on your bike.

You will have to trace the loom from stator to rectifier.

Also, there should be a brown wire and a green wire going from the alternator cover (field coil) to the regulator. Make sure that is not grounding out somewhere and they are in good condition.

When the voltage drops as you saw, the regulator will sometimes react with a brief over-voltage to recover. You do not want this happening with a lithium battery. The burnt out filament could be a sign... it could also be from vibration too, but you don't want to take chances.

loudhvx wrote: The 77 750 twin stator should have 3 yellow wires. You will want to look into why one is black/yellow. Maybe someone just replaced a bad yellow wire with a black/yellow one, or maybe the black/yellow one is not related.

Black/yellow is normally ground on all Kz's.
The rectifier and regulator are two separate units on your bike.

You will have to trace the loom from stator to rectifier.

Also, there should be a brown wire and a green wire going from the alternator cover (field coil) to the regulator. Make sure that is not grounding out somewhere and they are in good condition.

When the voltage drops as you saw, the regulator will sometimes react with a brief over-voltage to recover. You do not want this happening with a lithium battery. The burnt out filament could be a sign... it could also be from vibration too, but you don't want to take chances.

The unit that I replaced on the bike was a reg/rec combo. I just looked at the wiring diagram and youre right. There is also a regulator - a separate one. Why would the bike have had a reg/rec combo AND a regulator? and might you know where I can get a regulator? And would this be redundant?

It should not have both. If somebody replaced the old rectifier with a combo unit, and somehow left the old regulator wired in, I can imagine that could cause electrical weirdness.
The bike needs one rectifier and one regulator, they can be in a combo unit OR they can be separate units, but not both.

TexasKZ wrote: It should not have both. If somebody replaced the old rectifier with a combo unit, and somehow left the old regulator wired in, I can imagine that could cause electrical weirdness.
The bike needs one rectifier and one regulator, they can be in a combo unit OR they can be separate units, but not both.

thanks Texas...i just checked. it has only reg/rec. 3 wires from the stator to reg/rec: blk/yellow and two yellows. then a grey wire and red wire connecting to the harness

KawaKrazy wrote:

TexasKZ wrote: It should not have both. If somebody replaced the old rectifier with a combo unit, and somehow left the old regulator wired in, I can imagine that could cause electrical weirdness.
The bike needs one rectifier and one regulator, they can be in a combo unit OR they can be separate units, but not both.

thanks Texas...i just checked. it has only reg/rec. 3 wires from the stator to reg/rec: blk/yellow and two yellows. then a grey wire and red wire connecting to the harness

Those wire colors are not stock for the charging system. Maybe someone did some creative wiring before you got it. We would need to see better photos of the harness coming from the alternator area. There should be 5 wires: 3 yellow from the stator. 1 brown and 1 green from the field coil.

Luckily, you can get a regulator and rectifier from OregonMotorcycleParts.com.
They are one of the only companies out there that are truly aware of the charging system you have. It is a very unique charging system not found on any other Kz. It originally had a solid-state regulator to control the negative side of the field coil. Other Kz's with field coils control the positive side, so yours is opposite. Oregon knows this and has a regulator specifically for your bike, in case you need one.

Beautiful looking paint on your bike, by the way! That color really looks amazing!

loudhvx wrote:

KawaKrazy wrote:

TexasKZ wrote: It should not have both. If somebody replaced the old rectifier with a combo unit, and somehow left the old regulator wired in, I can imagine that could cause electrical weirdness.
The bike needs one rectifier and one regulator, they can be in a combo unit OR they can be separate units, but not both.

thanks Texas...i just checked. it has only reg/rec. 3 wires from the stator to reg/rec: blk/yellow and two yellows. then a grey wire and red wire connecting to the harness

Those wire colors are not stock for the charging system. Maybe someone did some creative wiring before you got it. We would need to see better photos of the harness coming from the alternator area. There should be 5 wires: 3 yellow from the stator. 1 brown and 1 green from the field coil.

Luckily, you can get a regulator and rectifier from OregonMotorcycleParts.com.
They are one of the only companies out there that are truly aware of the charging system you have. It is a very unique charging system not found on any other Kz. It originally had a solid-state regulator to control the negative side of the field coil. Other Kz's with field coils control the positive side, so yours is opposite. Oregon knows this and has a regulator specifically for your bike, in case you need one.

Beautiful looking paint on your bike, by the way! That color really looks amazing!

Thanks for the info. I already bought and installed a Regulator/Rectifier ESR600 For 1977 Kawasaki KZ750B/E~from ElectroSport Industries.

There are 5 wires, the are just different colors. 1 black and yellow, and 2 yellows from the stator, and grey and red from the field coil.

I was on the bike all afternoon and its fine. New 1157 bulb hasnt blown out yet lol.

What are symptoms of a faulty field coil, just in case.

That ESR600 reg/rec says it is 1-phase. The black/yellow wire is ground.
When I google it, it only shows 4 wires: 2-yellow, 1-black/yellow, and 1-white/red.
Here's the Link

That ESR600reg/rec (the 4 wire version) will work on a 1978 or later Kz750twin, though.

I attached an image of a 78 750 twin. Notice the alternator cover is different. The three missing screws means there is no field coil.

That ESR600 is not compatible with a stock charging system from 1976 or 1977 Kz750B1 or B2 twin. Even though they list it, it is not compatible. Their listing is wrong in many cases. They even actually list bikes that don't exist.

Your bike has the screws which indicates your bike has a field coil which makes the motor a 1976 or 1977. But then the ESR600 reg/rec I looked up should not work on your bike, at least not properly. You can kluge the field coil to work by grounding the green wire from the field coil. Then the alternator will be putting out full power all the time (as if it had a permanent magnet), then use a shunting regulator like the ESR600. But that is a terrible way to treat that alternator. It will potentially overheat the stator and the field coil, both, over time. It is not designed to work that way even though you can force it to.

When the field coil fails, the output voltage from the rectifier will reduce.

loudhvx wrote: That ESR600 reg/rec says it is 1-phase. The black/yellow wire is ground.
When I google it, it only shows 4 wires: 2-yellow, 1-black/yellow, and 1-white/red.
Here's the Link

That ESR600reg/rec (the 4 wire version) will work on a 1978 or later Kz750twin, though.

I attached an image of a 78 750 twin. Notice the alternator cover is different. The three missing screws means there is no field coil.

That ESR600 is not compatible with a stock charging system from 1976 or 1977 Kz750B1 or B2 twin. Even though they list it, it is not compatible. Their listing is wrong in many cases. They even actually list bikes that don't exist.

Your bike has the screws which indicates your bike has a field coil which makes the motor a 1976 or 1977. But then the ESR600 reg/rec I looked up should not work on your bike, at least not properly. You can kluge the field coil to work by grounding the green wire from the field coil. Then the alternator will be putting out full power all the time (as if it had a permanent magnet), then use a shunting regulator like the ESR600. But that is a terrible way to treat that alternator. It will potentially overheat the stator and the field coil, both, over time. It is not designed to work that way even though you can force it to.

When the field coil fails, the output voltage from the rectifier will reduce.

I spoke to the previous owner. Sheesh this guy is ... into it.

From what he said, though the 3 screws appear, he insists he made changes and that there is a 1978 motor in my bike - without a field coil,

Also, last night i found the problem. It was a grounded tail light wire which I missed the first time round. It was a bit frayed.