Gringo Bill is right  - When I got my Cobra I could not figure out how to adjust the speed of the servo.  Called Steve -  He told me the machine had to be running in order for the speed to change when you push on the arrow keys.  It is in a very ackward location to reach down around the pulley and do this while running the machine, but once you get it adjusted to a speed you like you don't change it too often.  Another hint I have learned,  If the machine starts to skip a stitch, you probably need to change your needle size.  If you are sewing on a thin leather, go down a size,  If you are sewing on thick leather go up a size.  Also check for any burrs on the needle tip.  These tips were passed on from fellow users and have helped me a lot.