In most cases, the thread has not been passed through the upper tension properly. If it bunches on the bottom, make sure the thread is pulled well into the upper tension disks (thread with the presser foot up so the tension disks will be open when threading). Also, you could make sure tension is set properly. Turn up the tension if thread bunches on the bottom of fabric. Try different tension settings to get a balance where stitches are about the same on the top and the bottom. You want upper tension tight enough so that the top thread pulls the bobbin thread up to meet and loop together making a good stitch.
Rarely would you need to ever adjust bobbin tension. Tension on thread is controlled by upper tension threading. This is true for all makes.
Rarely would you need to ever adjust bobbin tension. Tension on thread is controlled by upper tension threading. This is true for all makes.