Stephen M:
A couple of observations, not knowing how long you've had the Cubs.. One, normally, at low RPMs, the SG will not charge and the ammeter will show a discharge. Secondly, if you ran it for a couple of hours at high enough RPM for it to charge, and the battery seemed sluggish when you went to restart it, I'd suspect you've got a battery going bad, which will make the SG run hot trying to charge it. The battery should have been fully charged by then. Note it is normal for the Voltage regulator to drop out at low RPMs and the ammeter show a discharge.. Not charging at high RPMs, I'd first look at all the connections, including battery and VR grounds,and connections between the SG and the VR. I'd point more at the VR than the SG if there is a problem....