REL 7 NFS Server fails to mount more than 374 clients with nfsversion 4.1

We try to mount an REL 7 server from a 700 Node HPC cluster via NFS Version 4.1 ( the reason why it has to be Version 4.1 is a different topic to discuss, but for the moment we need NFS 4.1 with the exact-only-once semantics)
After 374 mounts the next client mounting the server stops in the mount command until one of the 374 unmounts again.
What can we do to configure the kernel to alow more than 374 mounts?

THX in advance.