as p-bar stated the rotophase tries to shove a third leg in between the 180* single phase. with your motor running use a amprobe to check current on each leg, it will instantly be obvious why the motor looses power. and as stated above the voltage to ground will be 120 volts for the single phase legs and 160 to ground for the odd angle, with no true 120* angle between phases the motor poles are not lined up for best efficiency