Motorcycle Repair: Electrical Drain low charging, honda cb 750, electrical drain

Question
I have a 1980 Honda CB 750 K.  I had the charging system repaired a couple years ago, and resently two different shops could not find a problem with the charging system.  The bike seems to have a slow drain which I haven't been able to trace.  I have been told that the charging system will only charge @ about 12.9 volts instead of 14 which causes it to draw on the battery even while driving.  Is this true?  If so, any suggestions?

thanks,

Answer
Bruce, it probably isn't a slow drain, it is just an ineffective charging system. You can download a troubleshooting guide from www.electrexusa.com to guide you.
Biggest problem with low output on these bikes is that the rotors go bad. Check the resistance values on the slip rings COLD and then HOT and you will often find that they go out of range when the engine warms up. Occasionally the rotors will shear the key and are actually spinning on the end of the crankshaft, but that is rare. Usually the biggest problem is getting them off the crankshaft. Be sure to use the correct special tool for removal. You can pull lighting fuses to isolate the charging system output, to ensure that the problem is output and not a draw, but there isn't much in the system to draw down the charging system other than the halogen headlight and running lights.
Make sure the brake light isn't staying on when testing.
If the rectifier/regulator and stator checks out okay, the problem is most likely the rotor.

Bill Silver