Motorcycle Repair: 1970 Honda CB360, rotor stator, current regulator

Question
I have a 1970 Honda CB360 that drains batteries.  I can put in a brand new battery, and if I let the motorcycle sit for two weeks without using it, then the battery will be drained when I go to use it.  I have had it checked numerous times at various dealers, and everybody tells me they can't find any source that is draining the battery.  Nobody has ever kept it for more than four days because they tell me if they can't figure it out by then they aren't going to be able to.  Where should I look first for my problem?  

Answer
Walter, either your bike is NOT a CB360, due to the date (made 1974-77) or your bike is a CB350, if it is a 1970 model.

Basically they are similar... permanent magnet rotor, stator, rectifier and a small current regulator mounted on the back of the battery box.

Assuming that there is no modifications to the wiring, which could cause a draw, the most likely candidate is the rectifier. It is permanently attached to the battery and the diodes prevent back draws of voltage when the bike is shut off. A damaged diode section will will either be an open circuit or a drain of the battery.

First determine if the charging system is fully charging the battery to full specs. Hook up a voltmeter and check the output at about 3,500 rpm. If it is about 13-15v, then the output is fine. If not, then the stator has to be checked for output on the three leads, with the pink one about double the output of the other two. If that is correct, then the rectifier has to be checked (finned box looking item, near the battery). You have to use an ohmmeter to check the leads and then reverse the leads to check the diodes in the opposite direction. IF you get the same readings on the same diode section, then it is damaged. If the rectifier checks out and the charging system is doing its job, disconnect the little silver module box which is the current regulator.

You can check for battery draw by disconnecting the battery lead (either one) and putting the volt meter or set it for amps and see if there is a draw when everything is shut off.

Go to www.electrexusa.com for their free troubleshooting guide for charging systems.

PS. BE SURE that you are turning the key to the OFF position when you shut it down. The key will come out in the PARK position., which turns the tail light on and that will run the battery down overnight... FYI

Bill Silver