There is an adjustment to adj the needle,it's the screw above the screw that holds the needle in,and you want to adj it so the needle is as close to the shuttle as you can w/o touching it.You might also try tightening down your foot pressure,the larger the needle & thread combo your trying to use will need more foot pressure to hold the leather down because if it doesn't hold down it can skip,loose gears & timing can also cause skipping,but you might as well start with what I mentioned & le me know what happens.
Bob