No generator is designed to charge the battery at idle speed. Your 6-something volts at idle is perfectly normal and there's nothing you can do to improve it other than installing a very small pulley on the generator to spin it faster at idle. Then it will try to throw the windings out of the armature at highway speed due to overspeeding of the armature.

The third brush is only used to control the maximum charging voltage against a fully-charged battery. It has a sliding mounting point that allows the brush to be moved toward or away from one of the fixed brushes. This adjustment MUST be done when running at fast idle, and against a fully-charged battery. Most of the third-brush systems I've worked with had to be run at the maximum output to keep the battery charged properly. Some of the newer 3-brush systems have a circuit that puts the generator into maximum output when the headlights are turned on. Good luck!

The cutout relay interrupts the battery-to-armature circuit, not the fields.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!