For FMQ, unless you have a Bernina (& then I have no idea) you need to set the stitch length to 0. That isn't because you are using small stitches, it's because that allows you to control the stitch length. Getting a uniform stitch length is not easy. I have heard many quilt teachers say that it takes 8 hours to get the motion down. That sounds about right to me. You need to move through the machine at a relatively fast pace so you don't end up with teeny tiny stitches that are just pinpoints & those are even worse to try & pick out. However, if you move too quickly, you will get poorly formed stitches & overlapping thread.
FMQ is like riding a bike. You can learn to do it in about a day if you want to spend the whole day practicing. From there, you just get better & better. One other thing I would suggest is maybe picking a wavier stipple. Straight lines with a darning foot are REALLY difficult to manage. Since you have the space, maybe try shortening the U shape to 2". The shorter stipple is easier & more forgiving. If you haven't already checked out Leah Day's YouTube videos, I highly recommend them.
http://www.youtube.com/watch?v=fFcIT...1F4B76430BB141
The only thing is that she now recommends
marking your quilting lines, whereas a few years back when she recorded these videos, she did not. Hang in there & keep quilting! If you practice on some junk fabric, you won't need to rip out the stitching when it gets all messed up like that. Start by raising the Top Tension setting by 0.5 to 1 setting (keep increasing in 1/2 increments until the stitches are formed properly. Make sure you are using the correct foot for your machine -- it should be an
open-toed darning foot. You also need to either
lower your feed dogs, or if you can't, get a cover for them (you swap out the regular plate for one that only has the needle hole). If everything seems to be set-up correctly, just keep practicing. You'll get there in no time!
PS -- Having a pieced back does make FMQ more difficult. It adds friction to your quilt. Because of this, make sure that you have a nice flat surface to lay your quilt on (the machine bed is not nearly big enough). Once you get some hours in & see if you like it, there are other little notions you can try that may help, but for now most of them would just make things more confusing. Start with what you have, get the top tension right & then just keep working at it. FMQ is super fun, but it is a skill & you need to build that muscle memory before it will look right.
Best wishes!
Bree