"COUGARNFW" wrote in message news:20040922022729.27462.00000414@mb-
There was an AD in '79 which made it mandatory for all Cessnas from the 140A
and beyond to install a half-vented cap, at least one, on either tank, leaving
the other non-vented cap on unless you changed both.

The 140 is a completely different deal. Some of the 140 the caps actually provide venting
in normal operation