Hey Mr P-D, First, from your one response where you were placing your ammeter between the generator output and the system, your readings between 7&8 amps idling, 4 amps running indicate your genny is working. The low speed output is fine. However, your high speed output is low, probably causing your difficulties. The third brush regulates the genny output by warping the magnetic field inside the generator, and thus giving a way to roughly control its output. Amazing, Warp drive in a WWII era motorcycle
Don't worry how that all happens, just be glad it does. At any rate, My first guess is that you have your third brush rotated almost fully clockwise when viewed from the left side of the bike. You should try rotating it fully anticlockwise, then moving it back just a small fraction. This should be a good place to start.
What you would like to see is a small forward (charging) current into the battery under most operating conditions. Typically, people measure this by breaking the circuit at the positive terminal and inserting the ammeter. However, you may also do this at the negative (ground) terminal as well. When measured here, you look for current flowing into the ground as a proper charging scenario.
Just as a point of reference, a 32E will output about 10amps max when measured at the generator, not at the battery. At the battery, you're only seeing what amperage is left after feeding all the electrical systems, ign, lights, stereo, etc.
Now about the Third brush. The third brush control performs in a semi logical manner. (Semi logical to Humans, the electrons are perfectly happy).
At its fully anticlockwise position, the generator will have the broadest power output range, ie a relatively flat output curve over a broad range of RPM's. As you rotate the brush clockwise, you begin to peak the output and narrow the output range. The peak will occur at lower and lower rpms as the brush is continued to be rotated clockwise. Like a hot cam in an engine in reverse! Ideally, you want to minimize the clockwise rotation to what will just give you the output you need.
Hope this helps, Go Forth and Warp.