Objective: Identify and correct the most common stitching faults on the Janome MC6650 so your finished items meet a quality good enough to sell.
Most stitching faults come from one of three areas: threading, tension, or the needle. Learn to read the fault from which side of the fabric it appears on. Loose loops on the BOTTOM of the fabric almost always mean the TOP thread is at fault — usually it wasn't seated in the tension discs because you threaded it with the presser foot DOWN. Always thread with the presser foot UP so the discs are open. Loose loops on the TOP of the fabric point to the BOBBIN — check it is wound evenly and sitting correctly in the case with thread running the right direction. Skipped stitches usually mean a dull, bent, or wrong-type needle, or a needle inserted not fully up and flat-side-back; replace it and re-seat it. Thread breaking repeatedly means tension is too tight, a burr or nick in the threading path, or a poorly wound bobbin — lower the tension number and re-thread smoothly. Puckered seams mean tension too tight or stitch length too long for the fabric. On the MC6650, use the automatic thread tension as a baseline (around 4) and adjust only one step at a time, testing on a scrap. When a seam is already wrong, don't yank it: slide the seam ripper under a stitch every few stitches, cut, then pull the thread free, and brush away the cut 'whiskers.'
Example: You sew two cotton scraps and flip the piece over: the top looks fine but the underside has loose loopy threads lying on the surface. Reading the rule — loops on the bottom means the top thread. You raise the presser foot, pull the top thread out of the machine, and re-thread the whole path with the foot up, making sure the thread snaps firmly into the take-up lever and tension discs. You sew a new scrap: the loops are gone and both sides show balanced stitches where the threads lock inside the fabric layers.
Try it: Sew a 10 cm straight seam on a doubled cotton scrap, then deliberately create a fault: thread the top with the presser foot DOWN and sew another seam. Flip both samples and compare the undersides. Note which sample shows loops. Then fix the faulty one by re-threading with the foot UP and sew a third seam to confirm it's corrected. Finally, use a seam ripper to remove your faulty seam cleanly without tearing the fabric.