Lots of mirror errors on yum

[Edmon Begoli]

Hi,

When I recently run yum install on my virtual Fedora 13 (my test machine)
I get into lots of 404 http errors on mirrors.

I suspect that this has to do something with this Fedora not
being as frequently updated as my physical one, so I would like
to know if there is something I can do with my yum to eliminate these
inaccessible mirrors.

Thank you in advance,
Edmon