Tension -  what is wrong?

If you take the time to work through the TENSION tutorial named Secret To Taming Your Serger ONE TIME, you will know how to set your own serger and correct your own tension settings forever. This helps you create a "stitch dictionary" for how your own machine produces balanced stitching:

Secret To Taming Your Serger

Relevant Tutorials

Adjust Presser Foot Pressure

DIBY's Serger Tension Guide

SergerPepper's Fabulous Serger and Sewing Tutorials

Serger Tension Tutorial based on a Juki but great detailed photos

Skipped Stitches

Threading Your Serger

Timing

Troubleshooting Noises