Originally Posted by
bdschafer
is the fabric on the bottom is being gather in as it sews??
If the foot pressure doesn't solve it, the bobbin tension may be too high. If the seam is stitching without obvious upper or lower thread loops, then both tensions are too high. I'd back both tensions off and slightly adjust each while test sewing. It could have been tensioned for a rigid fabric and a lighter fabric will bunch if tensions are too high. You will like the 401. Other than the old black beauties, the 400 series is my choice.