Motorcycle Repair: 1978 Honda CB 125S battery looses charge, charging system, battery

Question
My 1978 Honda CB 125S  the battery will not stay charged.
What needs to be done to fix this problem?

Thanks!
Kellt

Answer
Information on troubleshooting the charging system should be in your shop manual. If you don't have a shop manual you should get one - your bike is an antique and you will have a hard time finding a shop that will work on it. The sad fact is that a lot of the mechanics working now are too young to remember bikes this old and aren't interested in learning about them so that they can do a proper job. This means that you will have to do most of your own work, and working on a bike without a good shop manual is just not worth the headaches. (My bikes are from the same era - that's why I fix them myself.)

I recommend that you get two manuals - a Factory Shop Manual and a Haynes or Clymer. That way when you don't understand the explanation in one you will probably figure it out when you have read the other too. If you spend some time on Google you might even find a factory manual available for free download.

Here are some basics of what you should be checking for:

Charging system voltage - measured at the battery, this should typically be in the 14-14.5V range when the engine is running at the same RPM as when on the road (usually the voltage is much lower at idle).

Are all of the connections where the stator, rotor, regulator/rectifier &c plug into the harness clean and in good order?

How to check the stator, rotor, reg/rec &c should be covered in the manual.