I, too had this problem with my Janome 7700 Memory Craft. After multiple cleanings and needle changes I learned that 'thread delivery' played a key part in even and unbroken stitches. If your spool is stack wound, it must stand upright so thread comes off the spool horizontally, preventing twists. It simply unwinds. If the thread is cross-wound on the spool, it should deliver off the end of the spool. My machine has the capability of both deliveries. I simply use the bobbin spindle for stand-wound spools. There are several different spool holder stands on the market that can help this issue too. Also, some threads have a very slippery surface. Increase top tension for these. Hope this helps.