seam puckering

Hello!

I'm trying to make a pair of pajama pants out of satin crepe and I want to use a french seam.  My problem is that I'm getting a ton of puckering when I sew the seams on my practice fabric scraps, what can I do to get it to lay flat?  I've played with the foot pressure a little bit, and of course I am pinning and pressing, but it just doesn't seem to make a difference.  Also, I have tried lengthening the stitch a bit-- still puckering.  Any suggestions?

Thanks!

First, I would use a new sharp needle. There are "Universal" needles, but make sure you are using the "Sharps" and I would use the 70/10 size for this type of fabric.

The other thing is to make sure the fabric isn't being stretched while sewn. Even the fabric hanging off the back of the sewing machine could be too much and can cause it to stretch while being sewn. Try to have it as flat as possible going into and out of the feed dogs.

Also, don't be too hard on your self. If you look closely, even the store-bought items made from slippery fabric has puckers. 

Another thing you might want to check is your tension.  Loosen it up just a  bit and see if that helps.  Definitely use a new needle.  Also make sure you are using a poly or poly blend thread.  Cotton thread doesn't have enough stretch in it.  It can cause puckering in slippery fabrics.