Final answer:
The most common problem when serged stitches are not smooth and even is incorrect tension. Other possible issues include dull needles, overlapping fabric, and incorrect stitch length.
Step-by-step explanation:
When serged stitches are not smooth and even, the most common problem is usually incorrect tension. This means that the tension on the serger is either too loose or too tight, causing the stitches to be uneven. Dull needles can also contribute to the problem, as they may not be able to pierce through the fabric properly, resulting in imperfect stitches.
Another possible issue is overlapping fabric. When the fabric is not aligned properly or if there is too much fabric being serged at once, it can cause the stitches to be uneven. Lastly, incorrect stitch length can also affect the smoothness and evenness of the serged stitches. If the stitch length is set too long or too short, it can result in stitches that are not smooth and consistent.