JenelTX

I agree with the suggestions so far. Also, make sure that before you start sewing, you pull the bobbin thread to the top. (At least, I need to do this with my machine. It works better for me. I have a Brother PQ1500S.) On my machine, there are three little holes that you can put the top thread through. Play with putting it through more or fewer of the holes because this will impact the top tension, as well, and may help. Basically, you just have to keep trying different things until you find what works exactly right for your machine on this particular quilt. Then when you move to a different quilt, if you use different thread, different batting, or different needles, you'll have to go through the whole thing again. Practice on a sandwich!

margecam52

If the feed dogs don't lower, cover them with a piece of plastic (lid from a plastic bowl cut to size & taped over the feed dogs). Not knowing what Singer machine you have...nor if you are free motion stitching, or trying to just sew straight lines makes it hard to make suggestions. If you are free motion quilting...cover the feed dogs, and set the stitch length at 0...since you are controlling the movement of the quilt...you are also controling stitch length...so the stitch length can be at 0, which keeps the feed dogs from moving.
You need a darning foot for the machine...and even if you are free motion quilting...the foot must be in the down position to have any tension on the upper thread.

margecam52

All bobbin cases have a screw to adjust them with. I have the drop in bobbins on three of my machines...and I have adjusted all three when needed. If you have the black drop in bobbin case...there is a small screw on the outside of the case (you have to remove the case by taking the face plate off first)...it's usually got a colored wax over it...mine have green or blue...but used to have one with pink. This is to try to deter you from adjusting the tension. One warning...the screw is only in by about two threads on the screw...to adjust ...think of the screw as the face of a clock...and if the slot the screwdriver fits into is at 9 and 3 o'clock...to loosen the tension, turn the screw to the left only one hour...so the slot is at 8/2 o'clock. To tighten...turn to the right until the screw is at 10/4 o'clock...even less if you can. Sounds like it's not the bobbin tension, but your upper tension that is too loose...and as others mentioned...lower the presser/hopping foot to put tension on the discs.