pdqquilts

I have a Mega quilter 18x8..I'm frustrated..can't get the bobbin tension loose enough, userthe stitch reg. But it only works for an inch worth of stitching then a large stitch comes up. Can't find needles as local Viking dealer doesn't stock them any longer..my machine is only year old have done 3 quilts hoping a praying not to screw up a top that I have put so much time into..at this point this was a huge waste of money! I use same thread top & bobbin, but when holding bobbin in hand and drop to ck tension it won't even fall..loosened screw still nothing....any help greatly appreciated!