Most of the tricks involved with using invisible thread have been mentioned. The changes are necessary because invisible thread stretches more than other threads. This is what works for me: lower upper tension, wind bobbin slowly, wind bobbin only 3/4ths full (especially with plastic bobbins, winding more than that can distort the bobbin just enough to create problems). Also, it's very important to make sure the top thread is feeding properly. I use a thread guide behind my sewing machi
p.s. LOVE the quilt!