I am wondering if the pressure knob needs adjusting. If he was sewing leather he probably had the pressure knob turned up high because of the thickness of the leather. I would try to screw down the pressure just a tad, then sew on the same material that you will be using and if need be continue to lower the pressure a bit. that may work, I really don't know but it is worth a try. I keep my 15-91 set up for FMQ all the time and I just use another machine for piecing and STID quilting.