Singer, the company that patented the lockstitch sewing machine in 1851, made sewing history again in 2008 by releasing the computerized Singer Curvy with its one-touch needle threader. The Curvy also features a drop and sew bobbin system. Despite these threading advances there will still be times when you need to adjust the tension on your machine. This is something you can do yourself, without hiring someone to do it for you.
Upper Threading Problem
Check to see if the thread gathers and bunches on the underside of the piece you are sewing.
Turn the knob so that the presser foot is all the way up.
Turn the knob for tension to 4.
Bring the thread from the spool down through the tension channel then up the other side of the machine. Listen for the spring to engage when the thread goes in between the tension discs. Continue the process of threading without actually threading the needle itself.
Hold the thread with your left hand and pull on it. If it pulls without resistance, lower the presser foot. Pull on the thread again to determine whether there is resistance now. If you feel tension, then you have adjusted the tension properly.
Bobbin Threading Problems
Check your work. If the thread is bunching at the top of the piece, then you have a problem with the way the bobbin is threaded.
Put the bobbin in the case. Make sure that the thread's end points in a counterclockwise direction.
Pull the thread across the throat plate and draw it to the back of the machine.
Check to see whether the thread continues to bunch on the fabric. If it does, continue to the next step.
Remove the bobbin from the case and adjust the screw at the bottom, a little bit at a time. Reinsert the bobbin and check to see whether the problem persists. Continue to adjust the screw if the problem continues.