I have a Honda 1979 CB 750K. It wont keep battery charged. I have replaced the fuse box, stator, brushes, generator rotor, regulator/rectifier, and new battery. bike still wont charge battery at a loss of what to do next. love the bike got from grandfather when he passed. want to ride it again need help bad. at a loss of what to do
Linda, You or your mechanic needs to backtrack and see how each component is working within the whole system.
print out the chart and then follow each step/test until you get to the faulty component.
Check for excess current draw in any added accessories or aftermarket components, including a higher than specified headlight bulb.
Bad grounds can cause unusual charging system issues, too, especially if the bike has been repainted or powdercoated.
Faulty ignition switch bases can cause intermittent power problems, too.
Use of non-OEM Honda parts can give problems, if they are manufactured incorrectly. Rotors seem to be the main problems in many of these bikes. Test it when hot and cold to see if there are major changes in the rotor's resistance values on the slip rings.
Start with a fully-charged, load-tested battery first, then follow along through the ignition switch, harness wiring, stator connectors and generator lead connections. Strip off the fuel tank and seat, so you can check the whole wiring harness for signs of overheated wires, work/broken leads, bad grounds, poor wiring connections/connectors and general wear and tear of over 30 years of use. All it takes is one faulty wire or connector to compromise the whole system.
Sometimes, individual component failures will damage associated components in the process of failure, so unless you replace everything all at once, there is a chance that each new replacement part could be damaged from something else not found in the troubleshooting process.
Even spark modules can cause excess current draw as they go into failure mode. Everything electrical must be examined and tested for proper function.