NFS mount to non AIX hosts not correct

[Peter Mutsaers /1000000]

When I mount AIX filesystems (both AIX 1.2 for PS/2 80's, and AIX
2.2.1 on RT's) on other UNIX hosts (non AIX) I have the following
problem:

The mount succeeds and seems to work, but whenever I try to read more
than about 1400 bytes (probably more than 1 ethernet/tokenring block)
the NFS server does not respond anymore (timeout?) This happens on
various types of UNIXes that are able to mount correctly from each
other.

Do I miss some fixes, can it be a wrong configuration on the AIX side,
or is it an unsolved problem?
(please email reactions to me too instead of only posting, as I am
away for more than a week)
--
Peter Mutsaers                          email:    muts at fysaj.fys.ruu.nl     
Rijksuniversiteit Utrecht                         muts at fys.ruu.nl
Princetonplein 5                          tel:    (+31)-(0)30-533880
3584 CG Utrecht, Netherlands