Sewing Gurus, what do you think is going on here?



Sewing baffles into my UQ. Mara 70 bobbin and thread, Brother 6000i, 12 or 14 needle isn't new. Every time I get going a little fast, over half speed or so, I get a jam up. I'm getting near the end of the thread and it starts dancing around some when I get going fast, causing some slack I think...

Wonder what the culprit is likely to be?