searching for non ascii characters

[Radomir Hejl]

Hello,
when in a text mode, I usually use input method. I am able to find any character
with C-s. After saving and reading the file from a disc non ascii characters
cannot be found. When I do C-u C-x C-= on non ascii char before saving I see
a charset latin-iso8859-2. Doing C-u C-x C-= after saving there's usually
mule-unicode-0100-24ff or latin-iso8859-1 charset.

So now I can only search with success for ascii chars. What should I trim in
emacs so that the searching be efficient?
I already asked in comp.emacs with no response.

Thanks, Radek.