This really sounds like it is more of a needle problem than a tension problem. Try running the machine with no thread, is it binding anywhere? Is the machine being moved too fast so it does not have time to make a complete stitch before moving to the next stitch, and catching somewhere causing the break? It could be any number of things happening, try different fixes one at a time. I hate that this is happening as we all just want to sew and have fun not problems.