Proper set of bobbins and tension set up vs. fabrics will sew you satified.Also incude regular maintenance cleaning of the feeds dogs with a brus,also the shuttle assembly need sometime to clean.Some threads and fabrics chips accumulates in the feed dogs and shuttles assembly.In setting up thread bobbins the thread should be clockwise direction as you pull out on slot coming out to the bobbins (as you shown in my inserted image manual).The loop thread should be propely in the sequence position same like in the image refer to it.If you use cotton/ polyester fabric in the begining of trial set tension dial to No.3 and stich to No. 8 to 12 any convenient to you Use needle No. 14 .Posible make a record if you are sewing different types of fabric mostly silk fabric is hard to sew adjusting to lower stich can posible sew satisfactory.