Stop! Don’t keep sewing messy seams. They will just fall apart most likely.
Stop and take the time to get it right. Besides you can do a lot more damage trying to force it to sew when something isn’t right. You can damage the item you are sewing, or even worse your machine.
Don’t panic and call the repair people yet. Odds are good you can fix it. Don’t give up on sewing either. Consider it a learning experience. Every seamstress will wrestle with her machine once in a while. Talk nice to it, it helps keep your mood civil while you tinker. ;-) The more you do it, the better you learn your machine and eventually you will be an expert on that machine.
Resist the urge to go messing with your tensions if it was sewing properly the last time you used it. Smack your own hands away if you have to!! Odds are you will just mess that up.
Look for obvious improper threading. Check both the upper thread and the bobbin.
Rethread the machine. Upper and bobbin. Don’t partially do it...do it fully and completely. Sometimes the silliest things will be solved by a re-thread and you will never really “see” what the issue was. Be sure when you un-thread, you pull only in the direction the thread normally goes. To do otherwise will mess your tensions up. There is an exception when you get REALLY desperate. More on that later.
Clean the machine well with a brush. Avoid compressed air unless absolutely necessary. A brush is always better so you don’t blow fuzzies back into the depths of the machine. Not to mention canned compressed air kicks off chemical sometimes instead of just air. Not healthy for you or your machine.
When you clean it, remove the throat plate too. (The area your needle goes down into) You will be shocked at what accumulates there. Never underestimated the ability for fuzzies to ruin your tension and stitching. Clean it meticulously.
Re-thread the machine properly again for good measure. (seriously, I have re-thread what felt like a million times before..LOL)
Change your needle. Many people sew on needles too old. I am guilty of it too. Sometimes a needle will have lost it’s point or be bent to where your eye doesn't see it well visually. A bent needle will kill your stitching line and be messy. It can also damage your machine. For that matter, avoid sewing over pins. Many a lady has ruined her machine’s timing from doing that. At very least, only sew over them when you REALLY have to in a tight spot on something hard to hold. If you chose to sew over pins, don’t get mad at anyone but yourself if you kill your machine. If your needle hits a pin, assume at very lest it is probably bent with a dull point now.
Oil the machine, but only in the proper places and just a little as necessary. (see your manual) Make sure you sew on a scrap for a while after oiling. If you get too heavy handed with the oil, it can come up into your stitching and kill whatever you are sewing.
Re-thread it again. (You might be laughing...but I am serious :-)) For that matter, get a new bobbin and wind a new one. I have also had bad bobbin winding cause poor stitching. Make sure your bobbin is in it’s case properly and spinning in the proper direction (if you have a bobbin case for your machine). If you have a drop in bobbin, you still need to be sure you are putting in down there properly and in the right direction.
Then and only then go playing with your tensions if it still isn’t right. One exception to this rule. If you have small children always make a mental note of your normal tensions so you can see at a glance if they decided to play with the knobs and buttons. (guess what happened to me today!!!)
At your own risk on this one....but you can try flossing your machine. Not with dental floss, but your thread. Unthread the needle. Take ahold of the bottom and then grab the thread from behind the machine coming off of the spool. Gently and firmly move it back and forth just a little bit. You might find you dislodge a big ol’ piece of lint in your tension discs if your machine has those. Again, GENTLE!!! It is a risky thing. I was most prone to do this with my older serger where things would lodge in the tension discs regularly. More modern machines with computerized tensions, it is a really bad idea. So this one is very much at your own risk.
Finally re-thread your machine. ;-)
Do you have any tips to share? Feel free to share in the comments! I know some of seamstresses can be a bit opinionated on the matter. I would love to hear others thoughts on this one.
Add on tips from others:
You can also get a burr (sp.) on the throat plate from a broken needle that will cause havoc. They recommend an emory cloth for that.