Does your serger have 3 needles or 4? The 1st needle on the left is the needle for the seam that you are having trouble with. It may be the tension on that thread. One way to fix the seam is to sew over the serged stitchs with a regular machine. Serging if often used as a finish on regular stitched seams.
sunseak Thank You! Mine is a 4 needle, and I usually do have to go over my serged seams with the regular machine - but I've had people comment that I shouldn't have to do that. (like they never have problems with the threads showing through??) It makes me batty!
Check the tension on that needle. Sergers don't always have as flat of a seam as regular machines. They are designed for more stretch & give in the fabric. If it continues to bother you, ask the dealer you bought it from for troubleshooting advice. They might have a website to help.