[CentOS] how to disable slow repository mirror?

Using the yum-fastestmirror plugin on CentOS 5.

The mirror that gets selected seems to be always the same one, and the particular one for my EPEL channel is slow as sin (often 30 kB/sec or less). Ctrl-C moves to the next one which is satisfactory, but it's a pain to have to do that every time. Is there a way to prevent a particular mirror from being selected?

I can remove the entry from /var/cache/yum/epel/mirrorlist.txt, but it will come back at some point with a refresh.

Also, since the mirror is slow, why does it keep getting chosen, for all my machines?

Cheers, Tony Schreiner Boston College