You are a No Reply blogger so I cannot answer your email direct. Hoping that you read this. You describe in your email how you are trying to adjust your tension and nothing seems to work. The issue is that the bobbin thread comes to the top no matter what the adjustment is.
My machine has just come back from a 'major' service and the technician seems to have spend a lot of care and attention on the machine...it runs like a dream. Let's start with some basic things.
- you should run the same colour thread in the bobbin and on the top of the machine, so that minor irregularities from differences in speed when FMQ will not be seen so easily;
- you do not say what thread you use; I run Aurifil thread 50/2 in both the bobbin and top with a 70/10 or 80/12 needle (depending on what sort of project I am doing)
- if your bobbin thread shows through too much that means that the upper tension is too high pulling your bobbin thread to the top, so you would go and reduce the top tension and that usually fixes the problem
- my tension usually sits on 3.8 for the above thread/needle arrangement; if you need to go lower and lower to try to fix the problem that indicates to me that the bobbin tension might not be right.
Looking at the bobbin case of the newly serviced machine:
I am FMQ with that most of the time, but some time ago I have come up with a similar issue than yours which I have talked about in a previous post. I felt that the bobbin tension needed to be a little bit tighter.
I have got a second bobbin case, so I adjusted that one
You do not need to buy a second bobbin case...all it needs is for you to adjust your tension screw a little bit. Make a mental note (or draw a picture of where the screw sits, so you know where you started off) and turn the screw to the right slightly...go in small incremental steps until the tension is right. Given that it is the same machine, I would think that you only need to shift it a tiny bit if your tension screw looks like in the first picture.
Hope this helps