Usually if your needle won't stop going up and down when you release the stop motion screw it means the washer right behind the SMC is placed in wrongly. If I recall correctly, the three little bumps go away from the machine. There are two different ways you can place the washer this way, and one will be right. You will place it the other way the first time! So, put the washer on, screw the stopper into place, screw the little screw into place, and check it. If needle still goes up and down, unscrew little screw, unscrew stopper, don't let washer fall off (good idea to put the machine up on it's other side so the washer lays flat), move washer to other possible position, mark with sharpie, and try again. It should work that way. If all else fails, read the manual! Just did this a few days ago, though, and it worked.