Just a theory: Rich running engines will have heads that are too *cold*,
hence a higher temperature differential with the valve seats. Different
expansion rates of the 2 metals causes seats to drop.

If true, this may be of relevance to those who wish to replace their
precious FI with carburators. Discuss amongst yourselves... :)

-- 
Sami ('75 Westf.)
dakhlia@wuecona.wustl.edu
http://wuecon.wustl.edu/~samid/