This is a "basic" troubleshooting guide that applies to a majority of industrial sewing machines. If your machine problem or solution isn't listed here, please refer to the owner's manual.
Sewing problem 1: Skipped Stitches
Possible Cause 1): Lost timing
Solution: Re-timing the machine
Possible Cause 2): Thread tension is too tight
Solution: Correct thread tension
Possible Cause 3): Needle is bent or burred
Solution: Replace needle
Possible Cause 4): Needle is wrong size
Solution: Check needle size
Possible Cause 5): Needle and thread does not match
Solution: Use proper thread or needle
Possible Cause 6): Thread take-up lever has not been threaded
Solution: Check threading
Possible Cause 7): Light pressure on presser foot
Solution: Increase foot pressure
Possible Cause 8): Incorrect setting of needle
Solution: Check needle setting
Possible Cause 9): Material overlapped (cross seams/transversal seams, thickness of material changed suddenly)
Solution: Use specialized presser foot
Sewing problem 2: Fabric Puckers
Possible Cause 1): Stitch length is too long for material
Solution: Decrease stitch length
Possible Cause 2): Needle point is burred
Solution: Replace needle
Possible Cause 3): Incorrect thread tension
Solution: Check thread tension
Possible Cause 4): Light pressure on presser foot
Solution: Increase pressure on presser foot
Possible Cause 5): Fabric is too sheer or soft
Solution: Use underlay of tissue paper or under strengthening tape
Possible Cause 6): Using two different sizes or kinds of thread
Solution: Upper thread and bobbin thread should be the same size
Sewing problem 3: Irregular Stitches
Possible Cause 1): Incorrect size needle
Solution: Choose correct size needle for thread and fabric
Possible Cause 2): Improper threading
Solution: Check Threading
Possible Cause 3): Loose upper thread tension
Solution: Tighten upper thread tension
Possible Cause 4): Operator Pulling on fabric
Solution: Do not pull fabric guide it gently!
Possible Cause 5): Light pressure on presser foot
Solution: Increase pressure on presser foot
Possible Cause 6): Loose presser foot
Solution: Reset presser foot
Possible Cause 7): Unevenly wound bobbin
Solution: Check bobbin
Sewing problem 4: Loose bottom thread, bobbin thread Knots and Tangles
Possible Cause 1): Loose upper thread tension
Solution: Tighten upper thread tension
Possible Cause 2): Light pressure on presser foot
Solution: Increase pressure on presser foot
Possible Cause 3): The upper thread is too thick for material
Solution: Use smaller size upper thread
Possible Cause 4): Difference between upper thread and bobbin thread is too big
Solution: Using bigger size bobbin thread
Possible Cause 5): Bobbin does not run smooth inside bobbin case and shuttle
Solution: Use new bobbin case and shuttle
Possible Cause 6): Incorrect size needle
Solution: Choose correct size needle for thread and fabric
Sewing problem 5: Shorten stitch length
Possible Cause 1): Stitch length switch changed
Solution: Reset stitch length switch
Possible Cause 2): Pressure on presser foot is set too low
Solution: Check pressure setting on foot
Possible Cause 3): Feed dogs are lowered
Solution: Raise feed dogs
Possible Cause 4): Material overlapped (cross seams/transversal seams, thickness of material changed suddenly)
Solution: Use specialized presser foot
Possible Cause 5): Needle penetration power is not enough
Solution: Use more powerful motor or add speed reducer
Possible Cause 6): Climbing capacity of sewing machine is sufficient
Solution: Adjust the walking foot stroke or use climbing presser foot
Sewing problem 6: Machine does not feed fabric
Possible Cause 1): Stitch length is set to zero
Solution: Check stitch length and pattern
Possible Cause 2): Pressure on presser foot is set too low
Solution: Check pressure setting on foot
Possible Cause 3): Feed dogs are lowered
Solution: Raise feed dogs
Possible Cause 4): Threads are knotted under fabric
Solution: Place both threads back under presser foot before beginning to sew
Sewing problem 7: Sewing machine suddenly stops during sewing
Possible Cause: Sewing machine has been run at a low speed for an extended period of time. To prevent overheating, motor power will automatically turn off
Solution: Turn machine off for 20-30 minutes and the safety device will reset. Then you can continue sewing
Sewing problem 8: Upper thread breaks
Possible Cause 1): Threading is not correct
Solution: Check Threading
Possible Cause 2): Thread has a knot in it
Solution: Re-Thread Machine
Possible Cause 3): Thread tension is too tight
Solution: Correct thread tension
Possible Cause 4): Needle is bent, burred or has a sharp eye
Solution: Replace needle
Possible Cause 5): Needle is wrong size
Solution: Check needle size, replace if necessary
Possible Cause 6): Needle has been inserted wrong
Solution: Properly insert needle
Possible Cause 7): Thread take-up lever has not been threaded
Solution: Check threading
Possible Cause 8): Needle became hot and burned out thread
Solution: Add needle cooler or slow down sewing speed
Possible Cause 9): Material is too thick or hard, thread is not strong enough
Solution: Use better quality thread or big size thread
Sewing problem 9: Bobbin thread breaks
Possible Cause 1): Bobbin has not been fully inserted in bobbin case
Solution: Check bobbin case
Possible Cause 2): Bobbin has been incorrectly threaded
Solution: Correctly thread bobbin case
Possible Cause 3): Bobbin does not turn smoothly in bobbin case
Solution: Check if bobbin has been wound evenly
Possible Cause 4): Lint in bobbin case or shuttle
Solution: Clean bobbin case and shuttle
Sewing problem 10: Needle Breaking
Possible Cause1): Using too thin of a needle was for sewing a heavy weight material
Solution: Check Needle Size
Possible Cause 2): Needle has not been fully inserted into needle bar
Solution: Check needle
Possible Cause 3): Needle clamp screw is loosen
Solution: Check needle clamp screw and tighten
Possible Cause 4): Presser foot is not correct one
Solution: Check presser foot
Possible Cause 5): Presser foot is loosen
Solution: Reset presser foot
Possible Cause 6): Pulling on fabric as you sew
Solution: Do not pull on fabric! Guide it gently
