The thread tension is incorrect.
- Check the machine is threaded correctly. Rethread the machine according to the instructions in the manual.
Refer to "Upper threading" of "Preparation" category.
- Check the upper thread tension set.
- Remove the bobbin and make sure it is threaded properly in the shuttle race.
Refer to "Correctly installing a bobbin. " of "Preparation" category.
- If there is any loose thread or lint in the bobbin case, please clean them with the included cleaning brush.
Refer to "Cleaning the Bobbin Case" of "General Information" category.
- Check if the combination of needle size, thread size and fabric is incorrect. Be sure to use the correct needle and thread size for the fabric you are sewing.
(Example: Denim-size 16 needle and 40-50 heavy duty thread)
Refer to " Combination of fabric, thread and needle " of "General Information" category.
AS1430S, AS2730S, BM-3500/2600, FS101, FS155, GS2700, GS2786K, GS3710, Innov-is 10, Innov-is 1500D/1500, Innov-is 15P, Innov-is 30, Innov-is 35P, Innov-is 400, Innov-is 4000D/4000, Innov-is 4500D, Innov-is 50, Innov-is 55P, Innov-is 900, Innov-is 950, Innov-is 955, Innov-is 980D, Innov-is 980K, Innov-is I / Innov-is 6000D, Innov-is Ie, Innov-is V7, JS1410, LS-2125/2160, LX27NT, QC-1000, XL-2120/2220/2230/2240, XL-2600/2620/2630, XL-5500, XL-5700