I was looking at some diagrams I have for an Ed Gray type machine and I think I figured out what was happening. Say for instance your applying X% of energy to the capacitor. The first revolution around you get 25% of the original amount as back emf put into the capacitor. The battery will then supply another x% of power. Your capacitor now has 125% of the power it did the first time around. Now you get 25% more out of 125% as back emf. This will continue until the capacitor is fully charged. At that point the amount of instant energy provided to the device will be whatever the capacitor can handle. I'm just using 25% as an example. Essentially your using the motor as both a generator and a motor. I am not fully sure but it might be necessary to manually turn the shaft long enough that the capacitor can sustain movement of the device.
This also means it really isn't "overunity." The majority of the work is done by self generated electricity.
Eric