Not charging enough. Battery slowly dying.

1977 KZ650 B1.

Noticed my brand new battery slowly start to run out of juice over the course of a couple of weeks.

I hooked up the battery from my other 650 which was freshly charged. Fired up the bike and tested voltage at the battery terminals (please correct me if I'm doing this wrong). While the bike was running at idle it was sitting at around 12.6 12.7. At 4000rpm it jumped to 12.9, 13.0, which as I understand it is not enough to maintain the battery let alone charge it. Can anyone offer some suggestions or wisdom as to what might be going on?

Also, is it odd that my bike runs perfectly fine with a dead battery? I tried starting it and ran the battery completely out of juice to the point that the starter would not even turn over. But when I kicked it, it fired up an ran fine for the 20min ride home.

you should be between 14.5-15V at 3500+ revs.

It doesn't go past 13v when I rev it to 4000rpm, so something bad is going on. Can someone offer a suggestion as to what I should test? I've been reading posts and things are pointing to rectifier/regulator which are separate on this model.

Probably a wiring issue. Check that the battery connections are good, then where the output wire from the R/R goes to the Solenoid post. Also the Black/ yellow ground wire, clean tight god connection.
You can test just the AC side of your Stator for output. I suspect it will be OK If you are getting that much voltage already at the battery. You just need to find where the bad connections and voltage loss is at. Could also be where the Stator connects to the R/R.
The short battery cable from the solenoid to the battery can be the cause.
If checking AC at stator, 2 wire single phase will be 75 ACV, Three wire 3 phase will be 56 ACV on any combo of the three.
And as Patton says check the battery cable where it grounds to the engine block rear.

If it's not a connection or ground wire then it has to be either the reg/rect assembly or a bad alternator itself. That's about all there is in the whole circuit.

OK then the plan of attack is clean and ensure good connections. The if that doesn't work then I'll test the stator. If that is OK then on to the R/R. If I'm missing something please let me know. Thanks for the help.

One last thing, the battery neg post cable connects to the frame. Where is it on the frame?

IIRC the neg cable does not connect to the frame itself, but rather to the engine case. It connects via a screw / bolt just behind and below the oil fill plug on the right (as you sit on the bike) rear of the engine.

If the cable from the battery Negative(-) terminal to the engine bolt feels "Crunchy" when flexed, it's got internal corrosion and needs replacing. The same applies or the Positive(+) battery terminal cable.

I've been cleaning bullet connecters all afternoon trying to get to the root of my charging issue. Just to be clear and make sure I'm testing this thing correctly, I'm supposed to make sure my battery is charged, warm the bike up, attach a multimeter to the neg and pos terminal of the battery, and if I rev up to 4000rpm the reading on the meter should jump from 12.something to 14.5ish?

I'm asking because the fsm has a test involving two meters which I don't have.. and frankly I'm having a hard time figuring it out.

bloglos wrote: I've been cleaning bullet connecters all afternoon trying to get to the root of my charging issue. Just to be clear and make sure I'm testing this thing correctly, I'm supposed to make sure my battery is charged, warm the bike up, attach a multimeter to the neg and pos terminal of the battery, and if I rev up to 4000rpm the reading on the meter should jump from 12.something to 14.5ish?

I'm asking because the fsm has a test involving two meters which I don't have.. and frankly I'm having a hard time figuring it out.

Yes, you could try it at the battery first then somewhere else, maybe your headlight plug. The battery acts like a "voltage sink" of sorts and could potentially skew your readings.

Another thing- after you've cleaned your bullet connectors, shoot a little DeoxIt in there ( store.caig.com/s.nl/sc.2/category.188/.f ) which further cleans and removes corrosion and acts as a protectant.

Yep, I've cleaned all the bullet connectors which I can see are associated with the charging system, using de-oxit after to ensure proper connections.. there were a couple of suspect connecters which had some scoring which I replaced. It's still undercharging my battery. Revving to 4000rpm never gets it above 12.9v, so do you folks think it's safe to assume that either my rectifier or regulator are at fault?