The problems started with a new, same-thread spool - in the middle of a FMQ project that was going fine. The tension had been fine throughout. Now the stitches are skipping, OK enough on the front but so long and loose on the back. I've re-threaded a zillion times, tinkered with the tension anyway. Still skipped stitches ... What to do?

Change the needle.

and then do a bit of practice before you go back to the quilt.

try having the thread come off of the spool in the opposite direction :D:D:D

Make sure you have the thread and the bobbin threaded correctly. One missed step and it throws it all off.
Good luck.

Yes.... do all of the above.... I've had the same thing happen to me and it's always been one of these... Who would think the thread coming one side or the other would make so much difference?!

Also when checking your bobbin thread, clean the lint out, I use an old small paintbrush. I'm always surprised at how much lint there is after just a few hours of sewing with the cotton threads. Good luck

I had issues with my last fmq project... 1st spool was fine, 2nd spool kept breaking threads, snarling up... tossed it... spool 3 fine again

So if all else fails -- try some different thread and see if you are still having trouble

Loops on the back mean the tension on the top is off----silly question---did you put the pressure foot down?

Make sure bobbin thread is wound evenly...

Once again, you were right. I'm meandering like a maniac

Be sure everything is threaded correctly......

Duh! You did.

Is the thread spool damaged? Does it have a dent in it or anything. I read where damaged spools can affect the quality of your FMQ stitches.