Expert: Bill Silver - 4/19/2006

Question
I am asking this question for my dad, he has a Honda cb750 i believe the year is 1980.  The bike won't keep the battery charged.  He has to put it on the charger at night just to get to work then put it on the charger at work, and if the ride is longer than about half an hour or if he is traveling thru town at slower speeds the battery drains and the bike obviously dies.  I have been researching for him and what i gather so far is it might be the regulator/rectifier or the stator.  We are sure it is not the battery as he has replaced the battery twice in less than a year.  Your advice would be greatly appreciated thank you very much.

Answer
Katrinna.... First, do check to see that the battery will take a full charge and hold it. Repeatedly discharging them will damage the cells and continue to cause problems, even when everything else is okay.

Honda fours and six cylinder machines, from 1979 to about 1982 all had similar charging systems, which had numerous problems.

First, they had brush contacts inside the dyno cover, which can wear down, then you get no charging at all until they are replaced. Check the brushes first.

Second, the rotors tended to go open when they got hot, so even when the brushes were replaced the rotor windings wouldn't energize due to the high resistance or an open circuit. You need a special tool to remove the rotor, if that becomes necessary.

There is a stator, which is often not the problem and a regulator rectifier which can often be the problem. Go to the site below and download the troubleshooting chart for more assistance. You will need a volt-ohm meter to do testing on components and perhaps a 12v test light, as well.

http://www.electrosport.com/electrosport_sitemap.html
http://www.electrosport.com/electrosport_fault_finding.html

Bill Silver www.vintagehonda.com