nfs timeouts?! client or server specific?!

hi mailinglist, we have setup an autoyast environment which serves the installation data via nfs. we are facing the situation that some clients can't connect to the nfs-server (others do), the automatic installation process wents back to the manual installation menu. if we choose there network install and as source nfs the client find its way and can connect to the nfs install server, the installation starts and a "half automatic" installation goes on. how can we be sure that the client also connects to the nfs-server without going through the menu by hand?! are there any possible settings or parameters for the nfs-server or the client to change, may be timeout values or something like that?! thanks for answers. :-) helge.