Was getting a lot of

[Errno 12] Timeout: <urlopen error timed out>

with yum. Went into /etc/yum.conf and added a line:

timeout=120

documentation was in man page yum.conf(5).

That helped a bit, but fetching mirrorlists was still giving the Errno 12 timeout error almost instantly. Worked around that by just pointing the yum.repos.d entries at a particular mirror. Probably some bad interaction with going through tor/privoxy (necessary to work around some recent china telecom auto-blocking)