My Spartan sewing machine's bottom thread jams up ?

I have a spartan sewing machine that was given to me, and in trying to get it to sew, I am finding that the bottom thread will tangle up and jam the material into the feed dogs. The machine has been serviced and oiled. Also, we have gone over the threading a few times, and the top thread is still breaking. Not sure if that could be caused by whatever is going on with the bobbin or not.
Thank you so much if anyone can help, in advance.