I have a 1977 Sportster XLCH that has the engine driven generator and mechanical voltage regulator. Is there a way to adjust the field current at IDLE so the generator will put out a little bit more ?
The generator does better when the RPM's are increased.

 

A little more rpm always increases the generator output. That is the way it is with a generator. One of the reasons for going to an alternator was to eliminate this.

As far as I know, there is no way to make a generator put out more Umph when it is running at a low rpm (as in idling)
pg

 

PG is right the only other alternative you have is to either invest in an alternator conversion kit (which is really expensive!) or just sort of live with it and try not to stop so much :-)