Voltage variation

I've noticed that my headlight (and all other lights) tends to dim at idle, and noticeably brightens when throttling at any higher rpm. To be clear, the brightness stays constant whether at 2,000 rpm or 7,000 rpms, but when it's at idle (about 1,000 rpm) it is noticeably dimmer.

Would replacing my stator resolve this issue? Or could it just need battery replacement?

It could be the battery. How old is it, what type & do you keep it properly charged?
Have you done any voltage checks? After charging, it should be 12.6 VDC, but a good battery will be higher.
Poor connections or improperly sized headlight or bulbs are other things to check.

What you describe is normal for the most part but I'd check the charging system. With the engine reved up to 5000 rpm there should be 14.5 volts or thereabouts across the battery. If you have less than 14 or more than 15 that indicates problems. Of course, check the battery too a martin says too.

The voltage will increase as rpms increase, that is normal but the difference in headlamp brightness is hardly noticeable.

Assuming your battery is even half decent then probably cleaning up all your electrical connections / battery clamps / frame earths would almost eliminate this. Your lights will be noticeably brighter too. Any 30 year old bike always benefits from this.

From what I've seen with my KZ650-C1 over the past 40 years as long as the headlight isn't going too dim at idle what you describe is normal. I would not recommend replacing the stator. If the stator had a problem the lights wouldn't brighten up much when the engine revs above idle. Take a look at the Kawasaki Service Manual if you still think there's a problem. It has a section on how to test the charging system. Ed

Thanks for the replies guys, looks like one less thing to worry about. I was planning on replacing the battery anyways, but good to know it's normal.

SmokyOwl wrote: I've noticed that my headlight (and all other lights) tends to dim at idle, and noticeably brightens when throttling at any higher rpm. To be clear, the brightness stays constant whether at 2,000 rpm or 7,000 rpms, but when it's at idle (about 1,000 rpm) it is noticeably dimmer.

Would replacing my stator resolve this issue? Or could it just need battery replacement?

That's normal. The system voltage drops to 12V at lower RPM and runs up to about 1`4V above 2k RPM.

It also is a good idea to check the electrolyte level in the battery once in a while. If low be sure to use distilled water.

Barry2 wrote: It also is a good idea to check the electrolyte level in the battery once in a while. If low be sure to use distilled water.

Or get an AGM battery and forget the water.

Thanks for reminding me guys, I had been battling the internet for a couple hours yesterday trying to figure out what battery to buy for my old kawi.

I know the old-school distilled water chambers are tried-and-true for these old bikes, but I really can't find any discernable difference between any brands. Any brands to look at or stay clear of would be helpful. Does it really matter? Prices are eyebrow-raising low sometimes and makes me question quality of the batteries. A lot of odd brand names I've never heard of are everywhere.

Now I'm going to check out agm batteries, thanks TexasKZ.

.....and just to be certain....lithium batteries should not be installed in these old bikes right?

You are right that there are quite a few good choices out there. I have had really good luck with Yuasa and Interstate. Both are readily available near me and I have gotten really good service from the dealer.
I think you are also right about the lithium batteries, unless you have upgraded to a more sophisticated regulator.

Some of the Yuasa powersport batteries are made in USA, but I don't think they have an AGM for my bike.
I got a scorpion agm from batterystuff.com & it has proven to be an excellent battery so far. I also have a Ctek US 0.8 smart charger & VC97 digital multimeter.