You don't say which color is the bobbin thread and which color is the top thread.
Ah, yes. The blue thread is top thread leaving the white as the bobbin. I have indeed tended and checked both the bobbin and the case. I have not taken apart the upper thread tension - will give that a shot ( I have done this multiple times on other older machines.
The photos show the improvement progression, but it just doesn't deliver a nice stitch one would expect from an older machine. I have had numerous older machines with stitch quality leaving the modern machines lacking. I'm really hoping to get the same from this one.