Needle first
Denim and canvas want a 100/16 or 110/18 needle; leather wants a leather point (wedge) needle in the same sizes. A universal 80/12 skips and breaks on four layers of denim and gets blamed on the machine.
Presser foot lift and pressure
Definition
Presser foot lift
How high the foot rises above the plate. A high lift (some machines publish an extra-high position) is what lets you feed a jeans hem or a bag strap under the foot at all.
Adjustable presser-foot pressure lets you back off for thick layers so the top layer feeds instead of creeping. A walking foot adds feed dogs on top and is the single most useful accessory for layered denim, canvas and quilts.
Motor and feed
Domestic machines publish speed, not torque. A machine that holds speed under load is what you are after; in practice the mechanical heavy-duty tier and the Juki TL straight-stitch class clear denim and canvas. Upholstery and marine vinyl are industrial walking-foot territory.
Short answer
Change the needle, add a walking foot, back off the pressure. If it still stalls, you need the heavy-duty tier; if you sew upholstery weekly, you need an industrial.
