Check out my article in the Tech Tips section on 6 volt charging systems. it's got a pretty thorough description of the 3-unit regulator. The mechanical point setup right behind the "F" terminal on the regulator controls voltage. The spring tension on that set of points needs to be increased, either by turning the adjusting screw or bending the spring anchor, depending on which type of regulator you have. When charging against a fully-charged battery, (That's vitally important!) the regulated voltage should be between 9.0 and 9.5 volts. This will allow the generator to produce enough voltage to actually force a charge into the battery, instead of letting the battery discharge itself through the generator armature.
Once the voltage adjustment is high enough to charge the battery, you'll need to adjust the cutout relay, the unit behind the "Bat" terminal, so it closes the points at about 8.5 volts. It's going to have a closing voltage set at around 6.5 volts right now. The adjustment is done the same way, by SLIGHTLY increasing the spring tension holding the points apart, and slowing the engine speed down enough for the points to spring apart as the generator voltage drops below battery voltage. Gently increase the speed until the armature voltage comes up and closes the cutout relay points. The closing voltage should be slightly above battery voltage, (about 8.5V works well), to assure the battery gets charged instead of discharging itself through the generator. The third unit, behind the "Arm" terminal, is the current regulator. You shouldn't need to change its setting, as it should work OK with the same current limit as it had with the 6 volt system.
I grew up around the best electrical shop in Nashville, Tennessee in the 1950's and 60's, and my father absolutely refused to have anything to do with an 8 volt system. They cause nothing but trouble, and there's no reason whatsoever to resort to that tactic to make a 6 volt engine in good condition start properly. If there's enoug internal drag in a hot engine to keep the cranking speed down, fix the engine, don't screw up the electrical system!
Jerry
