KZ 750 Spectre Stops Charging As Bike Warms Up

As anyone experienced this? The bike will charge around 14 volts when I first start the bike. After about 15-20 minutes the system will no longer charge the battery. Went for a about a 200 mile ride this past weekend and when I returned the battery voltage was 11.5 volts. Both the stator and R/R are original. I checked the wiring from stator and it looks OK. The connector at the R/R has been replaced so everything is clean there. Checked A/C voltage at idle ~60 volts.

Is it possible for a stator to develop a short when it heats up? I will probably go ahead an replace the stator anyway but I want to understand whats going on.

Yes it's possible.

There are other things that can also cause similar symptoms. The failure I see most often is when the regulator/rectifier gets old, it starts to lose regulation at higher RPMs. At lower RPMs it will charge fine, but at highway speeds, it will slowly drop the voltage until it no longer charges at all. Then, when the RPMs drop back down to slower speeds, it will start charging again.

I would try to swap the reg/rec first before replacing the stator, just because it's more likely. Try a used one from a more modern bike, like an early 2000's Ninja 250 etc. You may have to swap connectors, but the reg/rec should be cheap on ebay.

I'd check the wiring going from the alternator output wires to the regulator/rectifier, for signs of pinching and vibration damage. Most wiring is routed behind the sprocket cover, with "Bullet Connectors", check these for corrosion. too. If the wiring is twisted, un-twist them, looking for shorting between the phases.

From Z1E's listings:

www.z1enterprises.com/ItemDetails.aspx?i...+KZ750&item=RI10-305

www.z1enterprises.com/ItemDetails.aspx?i...n+unit&item=RI10-515


Good Fortune!

I have a spare R/R from a 750 spectre that I purchased from ebay. The bike does the same thing with both R/R's, charges when cold and then quits charging the longer you ride. It does not seem to be a function of RPM but of temperature. When dealing with 30 yr old electronics, I guess I could have 2 bad R/R's.

Patton - the links you posted don't work -- item not found

almarconi wrote: ...Patton - the links you posted don't work -- item not found

I refreshed and tested the links. Please try again.

Good Fortune!

Battery voltage was down, or charging voltage was down? After your ride. If charging voltage is down, I would check with all connections hooked up, voltages. The ACV at the stator 3 yellows just before the R/R, The Red/white charge wire close to the R/R, and while hooked there move the ground for your DVOM from the battery - to the R/R as close to unit as you can. If you have the 6 wire R/R unplug the Brown voltage sense wire, and be careful as voltage can surge to 18v at the battery.

almarconi wrote: I have a spare R/R from a 750 spectre that I purchased from ebay. The bike does the same thing with both R/R's, charges when cold and then quits charging the longer you ride. It does not seem to be a function of RPM but of temperature. When dealing with 30 yr old electronics, I guess I could have 2 bad R/R's.

At one point I had about half a dozen spares for my 81, all vintage. More than half showed the RPM-related symptom to some degree. At least two or three were not useable. The problem comes on gradually with age.

I should also mention, as the RPMs drop, the voltage recovery is a little slow, partly because the battery voltage will have been low. If the voltage does not recover when you let the RPMs drop to about 2000, then your issue is likely different from the one I'm describing, and may be heat-related as you said. In that case I would start with the bullet connectors under the sprocket cover as Mfolks suggested. Also, that is a good point to test the alternator resistance and AC voltage tests like the manual will describe.

The test Motorhead suggests, (of disconnecting the brown wire at the regulator,) is a good test to rule out the RPM-based failure mode I'm describing (because it disables the regulator's reference voltage). As he said, though, it's a dangerous test, so you really have to eyeball the battery voltage with a good meter. If the voltage is low, but then comes up fast after the brown wire is disconnected, then the stator is good, and the regulator is bad. If the voltage stays low, then it may be the rectifier portion of the reg/rec, or the stator, or the wiring. The rectifier portion usually fails fast and hard, though.

This could be a Bad Battery also. Is the Battery in good condition, full of electrolyte and tested to be sure of its condition?

This could be a Bad Battery also. Is the Battery in good condition, full of electrolyte and tested to be sure of its condition?

The battery was purchased in April 2012 it is a big crank agm battery. I will go through the wiring
again. When I did my initial check of the charging system, the brown sense wire was about 1 volt below battery voltage with the key on. I would think this would cause an overcharge condition. There is probably corrosion in the ignition switch, I don't know if this can be taken apart and cleaned. I will try to find a switched hot wire that is closer to battery voltage with the key on. A new stator should be here today so I am going to install it and see what happens. If I need to install a new R/R, I will probably go with a FET R/R like the Shindengen. I'll run the R/R output straight to the battery through a 30 amp fuse and do away with the sense wire all together.

You are correct that if the brown sense wire on the reg/rec has less than battery voltage, you will get an overcharge condition.

If the reg/rec has a sense wire requirement, doing away with it means the regulator can't regulate.

Had a chance to work on the bike this weekend. I was able to reduce the voltage drop on the brown wire to within 0.5 volt of battery voltage. Took the ignition apart and cleaned everything. Installed a new stator. The original stator looked pretty toasty compared to the new one. The old one was also pitted in the area that faces the rotor. Battery voltage across the terminals @ 5000 rpm is now 15.1 volts. The manual specs 15 volts at that RPM.

I am probably a bit overcharged because of the sense wire voltage difference. Probably would need to replace the harness to get a smaller difference on that sense wire. Didn't have a chance to take it for a ride but if it continues to charge after 30 minutes then I feel confident that the stator was the problem.