There is another reason as well, and not one you will find in the sewing machine manual.
This is a little known fact. I use the threads that are marketed as "good quality"and was sewing with the above reel yesterday. And noticed that the odd stitch was being skipped. It didn't matter on what I had done, but I wasn't going to keep going.
I replaced the thread with a new reel of a different brand:
I learnt this some years ago when I used to hire an industrial machine. (yes, I have a past life in sewing). I was grumbling about problems with stitches and thread breaking and was told it was the thread. My mother also had an experience like this - she uses a domestic machine. She has stitch problems and was told to use a "good" thread. She uses the recommended by all shops brand - which is quite different from that used by sewing professionals. Trouble is, you have to buy that by volume.
So, I now use the home sewers "quality brand"and have found one of these works better than the other on my machine.
I just thought I would share this in case any of you have had similar problems that have not been solved by changing needles and rethreading the machine correctly.
Sarah Liz :)