There's a known issue with starting virtual machines with large hard drive images. Apparently, the time-out is 3 seconds, but in reality, it can take up to 15 seconds for a machine to start. I've read several bug reports, and people confirming it's a time-out problem, but I have yet to see a solution.
Is there an option I can pass, like:
virsh start MyMachine --ignore-timeout
Or a config file that needs changed?