Your top stitching looks to be a bit tight.
You didn't say what model machine this is so I'm going to use the SWAG method.
First, go here to TFSR and read about adjusting tensions:
{
http://www.tfsr.org/publications/tec...machine_manual }
They have very detailed instruction on how to R&R, clean and fix tensions.
Second, check under the spring on the bobbin case or shuttle. It can get dirty under there, then the bobbin tension won't be right and the top will be too tight. Once the bobbin case is totally clean run the tension screw in until it stops then back it out a turn. Put a full bobbin in it and thread it. Then hold it by the string and let the bobbin case with bobbin hang. If it just falls away it's too loose. If you give the string a little jerk the bobbin should fall away a bit.
When pulling the thread you should feel just a bit of resistance, but not much.
When I have a machine that's being obstinate I usually find that when I get the bobbin right the top will fall into compliance pretty quickly.
Oh, and be careful if you do toss it out the window, you might sprain your back.
Joe