I have a Necchi 537L it was sold as a comercial machine that could do leather. Mine wont do soft paper! Whats up?

This is not a commercial machine and will give you trouble trying to sew upholstery,especially if you use heavy upholstery thread. You will get loops on the bottom.
It will sew only short stitches,No matter how long the stitch length is, because it only feeds the fabric from the bottom and it will stick.
It should sew regular fabric with normal threads with no problems. There is a pressure adjustment on the top of this machine which may be where your problem is located.Look in your book for instructions.Also, make sure the feed dogs are in the highest position. I don't know how long you've had the machine but if it has been awhile,remove the needle plate and clean the lint out from between the feed dog teeth.
sewman7