I have a 1983 Honda CB550C, that runs great, but I am having issues with the battery not charging. I have replaced the battery and rectifier. On a fully charged battery 12.6 volts, I start the bike and the voltage immediately drops to 11.99volts. taking the engine to 3000plus for a period of time changes the voltage very little to as high as 12.08volts. Does anyone have any ideas other than a new alternator coil what my problem might be. Where would be a cost efficient place to order a new coil assembly if needed.