before messing with the tension- try a different thread- some threads simply will not work for quilting- and you can spend days of aggrivation- and really mess your tension up to the point of having to take it in to a shop- when all you needed was to change to a different thread-
i have $400 worth of sulky rayon threads in 2 wonderful large sets- great for embroidery--
not a single spool will work for me for quilting- they all break...every couple inches.
so before messing with the mechanics of the machine start with a different thread and see what happens.