Ragged stitches- any ideas why?

I'm not a novice sewer, but I am fairly new. Recently, I've been experiencing problems with my stitches. When I'm sewing multiple layers, the "wrong" side looks ragged, almost zig-zaggy. The "right" side looks fine.

When I sew a strap together by putting a light interfacing and folding in half and then in half again (4 layers of fabric and interfacing) and stitch along both sides, it looks okay. But when I topstitch a bag (1 layer of interior fabric and fusible fleece and 1 layer of exterior fabric- I get these horrible stitches on the inside of the bag. The tension adjustments are where they should be, I think.

I guess I'm just trying to figure out if my machine needs repair, or if there is anything I can do to help this situation, or if it's just me.

Thanks!

Try using a bigger sized needle.  4 layers is a lot to go through and a bigger needle (#14 or #16 denim) will help.  Also try lengthening your stitch.  My preset on my machine is 2.2 which really is a tiny stitch...if you think about what the thread has to do vertically to make that stitch, it will appear longer when you sew 2 layers of a lightweight fabric like muslin than 4 layers of interfacing and whatever else.  It takes more thread to get through all of those layers to make a decent looking stitch.  With 4 layers, I would lengthen the stitch to 3 or 3.5 in length.  HTH.

Hi!  This may or may not apply to your situation, but have you cleaned the bobbin case?  The fuzz that gets in there can make your stitches goofy.  Your machine's manual should have the instructions for you.

Hope this helps.  This is a good tip for all of us...

Thanks, both of you. I usually use a 14 on the thick work, and lengthen the stitch to 3, but it almost seems the longer the stitch, the more ragged.

I will definitely look into cleaning the bobbin case, thanks! My manual is not very good, unfortunately.

I've been working on sewing machine for 25 years, here's my suggestions
change needle
adjust the top tension
& see if that helps