Most recent assessment: It struggles to stitch as a result of flat felled seams on denim denims or anything thick/major. Something, and I do not really know what, triggers it - but sewing along then all of a sudden it's such as the foot pedal The problem in this article https://sewingmachinestoreboulder86284.angelinsblog.com/1662175/boulder-colorado-sewing-machines-fundamentals-explained