My turn.

I have been through **** like this and I TINK I can tell you what to do.

Mrchanical regulators that use a relay can develop a fault which mak3s the spring stronger. Many of these have a screw setting to set the voltage, but the spring is too strong to allow the current to flow to the field of the alternator (or generator).

The cure is to reduce the spind pressure, and that is done by one of two way. One, if possible is to bend the tang to which the spring is attached to reduce its applied pressure. The other way is to overextend the spring to do pretty much the same thing. In each case, you will have to adjust the contacts to prevent overcharging.

Some of these regulators were SPDT, and the ideal was at idle the points would be closed at idle, putting the alternator or generator into full output mode. However it didn't always work out. Q@hen the RPMs increased, the contacts of the relay were supposedd to pretty much vibrate. This of course reduced their lifespan and then they had to be replaced. And plenty of people who did not know electronics errantly replaced many alternators when what they reall need was the regulator. Not all the time but enough worth mentioning. I am from a car family, I can BUILD a car from scrap metal.

Take the cover off the regualator and do not **** with that screw adjustment. Look where the spring attaches and bend the tang to reduce the pressure.

If it has an electronic regulator, you either need brushes in the alternator or simply to up the idle a bit. It really doesn't cost alot to up the idle. Someone mentioned a smaller pulley. well that might work but then when you crank it up to do real work it will wear and tear on the alternator by orders of magnitude.

Actually the easiest way out of this is to just crank up the idle speed until the thing actually charges and be done with it.

I got a lifetime of experience with **** like this and that is my recommendation. Take it or leave it. Just turn the damn idle up and forget it.