I don't think that kernel-devel installs the full kernel source, but just enough that you can compile and build kernel modules.
The full kernel source is in the source repos. You can download the source rpm file without installing it using yum downloader..
Code:
yumdownloader --source kernel
then you can build the dependancies
Code:
su -c 'yum-builddep kernel-<version>.src.rpm'
then install the kernel source
Code:
rpm -Uvh kernel-<version>.src.rpm
or alternatively you can enable the source repos (you would need either fedora, updates, and updates-testing depending on kernel version) and install the kernel source