OK- - - -one final test. Charge the battery- - - - -unless you plan on driving a couple of hundred miles without shutting the engine off, the generator isn't up to the task of fully charging a 6 volt battery. Once that is done, do the voltage check at fast idle again- - - -you should see 7.5 volts +/- a couple of tenths of a volt. This test MUST be done against a fully charged battery. If you don't get a good reading, carefully increase or decrease the spring tension on the regulator coil behind the "F" terminal of the regulator to get the charging voltage right.
Jerry