Hello Janet,
If the machines sews perfectly and then every now and again you get the loop it may well be the point is off the needle, it only take a small piece to break off or even burr over slightly, make sure you do not have any lint stuck in the bobbin case where you pull the thread out also.
drivewithken@blueyonder.co.uk
Ken
drivewithken@blueyonder.co.uk, November 2007