Battery dies after sitting in the bike for a couple of days. Could it be a short?

Question

I have a '73 CB350 twin that just recently started giving me electrical problems.

The engine was intermittently missing and after checking pretty much everything else, I replaced the battery. That seemed to fix the problem, which kind of surprised me because the old battery tested good.

Things worked fine for about a week (maybe 40 miles of riding), but now the new battery won't hold a charge. If I charge it up and let the bike sit for a couple of days, when I come back, it's deader than a doornail (~50mV).

I'm almost out of ideas here? One thing I noticed was 40-50 VAC coming off the regulator and into the rectifier at idle. I'm wondering if my regulator is fried since I think it ought to be getting 12-14.5 VAC going into the rectifier. But that would be overcharging the battery, wouldn't it? Electrolyte level looks good so I'm not sure. Maybe a short somewhere?

Answer 1

There is most likely a short somewhere in the system.

Answer 2

Test the battery.
Fully charge it and check the voltage.
If it's still in the bike remove both wires.
Check the battery's voltage in a day or two.
If the voltage dropped, the battery should be replaced again (it won't hold a charge).
You're right about the voltage.
Some Hondas had adjustable regulators. Does yours?
Change the regulator and check the out-put.
If it's normal again, test the rectifier with an ohm meter.
It could have been damaged.

Answer 3

check the selenium rectifier (this is mounted under the seat--it should be an orange thing with "fins"), these do go bad from time to time. Next, if both the battery and rectifier check out, I'd check the stator to ensure the charging system is working properly. If you don't have one, get a manual on the 350 and follow the test procedures. It'll guide you through the testing process pretty well

Answer 4

With the ingine running, place a voltmeter across the battery terminals and take a reading. If you are getting anything other than the 13-14VDC then take a look at the regulator. If the regulator checks out, then with the engine off pull a battery lead and place an ammeter in series. Then you can start disconnecting wires until you find what is causing the current drain. good luck.

Answer 5

let me walk through you with this, OK?the bike is DC. there is no AC any ware. Now, take the negitive clamp off the battery and then charge the battery. remember now, don't let that negative clamp touch any thing. after charging, let it sit over night as is, with that cable still off.

next day, take a battery reading. 13.5 volts DC is ok- 12 volts is good to.if the battery's charge has held ok over night, may indicate some thing is draining the battery, while it's sitting there.
reatach the negative cable, and start the engine. battery should read 14.5 no higher or lower.14.5 also proves the charging system is working as it ought to.

Answer 6

You bet!