This has got me stumped... I have a 1975 CB750. I have a charging problem that seems to be heat related. I have a voltage meter on the bike. On cool days (70 degrees or below), no problem, charging voltage is 14 or better. On warm days, the charging voltage starts off OK, but as I ride (and the engine temperature increases?) charging voltage gradually drops into the 12 volt range. I have one of the old right handlebar switches with a headlight On/Off switch, and if I turn the headlight off, the voltage jumps up about one volt and then gradually gets higher, but never gets above 13.5 volts. As soon as I turn the headlight back on, the voltage drops.
I have changed the stator (three times), Installed an electronic voltage regulator, a new rectifier, replaced the fuse box and the ignition switch and changed out the wiring harness (twice!). Some of these changes (the fuse box and ignition switch) did improve things somewhat, but the general symptom of a heat related voltage drop remains.
My latest theory is that there might be a high resistance short in one of the handlebar switches for the headlight - either the On/Off switch on the right side or the Hi/Lo beam switch on the left. Perhaps a connection that is almost touching ground, that expands slightly as it heats up and becomes a lower resistance short, but not quite shorted enough to blow a fuse. But this seems like a stretch.
This has been an ongoing problem for 4 years now. Trouble shooting tips or possible problems and/or solutions will be greatly appreciated.
