Daniel,  The transformer may be braeking down under load.  Test with your digital multimeter on Amps setting.  Make sure the leads are in the right spot (different terminal on meter to when testing voltage, continuity or resistance) and that you test it in series (both leads of meter in series with the motor , i.e one lead on positive from transformer and other on to motor.  You could do this with both transformers to see differance.