mule : multibyte to 7 bit conversions

[nospam55]

Hi

since I passed to emacs version 21.2.1 on Redhat 8  I noticed that in Man mode 
(or at least after M-x man RET bash RET), looking for hyphens with C-s didn't 
work; 
same problem even  when saving that man page on a file.

After some attempt I saw that with 

    (toggle-enable-multibyte-characters nil)

an innocent  -c  became visible as \234\364\370\262c  , and so on ; 
Mysterious utf8 proposals arose from attempts to save the manpage...

How can I bring this multibyte manpage into ordinary 7 bit ascii form ?
How to have manpages under emacs 7 bit by default ?

   Thank you :-)