8V is a bit too high. You'll end up boiling the cells dry on a long haul drive. The recommended upper limit for a 6V charging system is 7.5 volts, which is adjusted by changing the spring tension on the set of points behind the "F" terminal of the regulator. Lower tension- - - -lower voltage. Always adjust a regulator against a fully-charged battery- - - -overnight on the charger at least before trying any adjustments.

A quick battery test can be done at home. With the ignition switch off, crank the engine for 15 seconds. Check the battery terminal voltage while still cranking. A good 6V battery should not drop below 4.5 volts after 15 seconds of cranking and it should return to 6 volts or more of terminal voltage when the cranking stops.
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!