Check to see if your bobbin case has been dropped. It may be bent or there may be lint in it. Put your bobbin in the palm of your hand or on a flat surface with the thread coming off counter clockwise (to the left), then place your bobbin case ontop pull your thread through the slot and under the spring.
I have a Avante and have no trouble with it except when I mess up the bobbin. To save me lots of trouble with the bobbin tension I purchased a Towa bobbin tension gauge, a life saver and recommend it highly.
Good luck.