Believe it or not the two stitches above were both sewn whit the exact same stitch, tension settings and speed. So why do they look so different? Propper Feed technique. It is more important than it sounds..
The top is how the stitch is supposed to look (a tripple ZigZag) the fabric was fed through the machine gently from the front. The bottom seam was fed by pulling the fabric from behind the needle. By pulling, even slightly you are not allowing the feed dogs to advance the fabric at the proper speed and therefore the needle’s timing will be off from the fabric feed and causing missed stitches leaving an erratic pattern as shown above. In addition to a sloppy look and less strength in the stitch, you also run the risk of breaking your thread and or needle when you pull the fabric.
Trust me, it is hard to resist the urge to pull the fabric through faster especially at 3 am when you are tired and just want to be done already, but slow down and save your self time in the long run. No one likes to spend anymore quality time with their seam ripper than absolutely necessary! 😉