I have a max download speed of 200 kB/s, but currently I'm only downloading at around 20. However, this changes a LOT.

It even went up to 300 once, and sometimes just stalls at around 10 or something.

I'm using transmission on mac OS X. In the preference panels, the port is closed, it doesn't matter what I change it to. My router, provided by my ISP doesn't provide port forwarding. (It's "user friendly", I've been told the best change is to find custom firmware...or just buy another one).

Why does the speed change so much? Sometimes it's really fast for a while, so that seems to mean a barrier is gone. Though it goes up to 300 kB/s may be some sort of error on part of the ISP...

Seeds to leecher ratios of torrents are around 0.75. One was even 5 to 1, but had an average speed of 0.1 kB/s ....

What's the problem? (The average speed of 30 kB/s is still rather useable...for small things)