If you can't adjust the third brush to get a small positive charge with the headlight on at road speed either the genny has a problem or the lighting system is drawing too much it must show a slight charge. To check the grounding measure voltage with a good digital meter from Generator output to generator ground then to the frame then to the battery neg terminal if they are all within a few tenths of a volt of each other the ground is fine. If the ground is good hook an ammeter in the generator output wire turn on everything and rev it up. Does it put out what it is rated at? If not you have found the problem. If it puts out rated amps or pretty close put the ammeter in the head light circuit and see what it draws.