zimitt

Try rubbing the needle with some fine 600 or 400 sandpaper to make it slide through the leather easier. The matte finish will help it glide through the leather and catch the bottom thread.

I realize I'm way late to this game, but maybe this could help others. I don't have the heavy duty leather machine. I sew on an old Elna SU that will surprisingly deal with some very heavy leather, quite well. I was having the same problem of skipping stitches and the leather catching on the up stroke, lifting the presser foot and bouncing. Took me the longest time to resolve, but I'm pretty pig headed. I finally found a solution that worked great. I removed the needle and used 600 grit sand paper, sanded the length of the shaft and the entire surface of the needle. This creates a matte surface as opposed to a glossy sticky surface and was just enough to allow the needle to slide through the leather without getting hung up and lifting the work on the up stroke, resulting in the bottom thread not catching, and a skipped stitch. Also because there is not the drag on the needle and thread, there is a better tension result. I equate it to the difference between sliding your finger along a glass surface, and a brushed stainless steel surface. What also helped was moving the position of the needle to the far right of left of centre. If you have that option. Hope this helps someone.