My Book Live Duo works very slow on OSX Time Machine

My Book Live Duo works very very slow with Time Machine on OS X Mountain Lion. When I copy a file using Finder, the file or files are copied very fast. But when a programmed back up start, files to be saved on Time Machine are transfered very very slow. (2GB ± 2 hours) If I try to use Disk Utility, when Time Machine is running, Disk Utility application crashes. If I restart the disk, the back up work fast. But the next time, the backup, work again slow.
How I can fix this?

Sorry my bad English.


What’s the transfer rate your getting when you use time machine and when you copy the files manually?

When time machine is working, I don’t see the transfer rate…