craftgrrl | Sewing machine question

I know nothing about sewing machines. I'm lucky to have projects come out because I'm stubborn and also don't use patterns. Anyways here is my problem:

I have a Swinger sewing machine that I got about 4 years or so about for Christmas.

While sewing the thread, somewhere around the arm, will get super tight and then jerk hard enough to spool the spool of thread around a couple of times. If I'm lucky, the thread won't break but of course 4 out of 5 times that this happens, the thread breaks at the needle. Apparently the tension that builds and then jerks is too much and it breaks the thread.

I have adjusted the tension and I have also made sure everything is threaded through correctly and that the bobbin underneath is pointed in the right direction.

Does anyone know what causes this? I think I have narrowed it down to the section where the arm goes up and down (yeah I'm sure that helps) above the needle.

Question number two: While sewing, everything looks great on the side I'm sewing on but there are times I'll turn it over and it looks horrible! The thread looks all clumped up and tangled but it's still sewn together. Sometimes it'll even have black stuff like oil on it. The oil, I don't care because I'm sure it just needs to be cleaned but what causes the thread to look so tangled on the other side of the fabric?