Which file to edit to change the listening port?

I’m developing on my local server a website and I want to change the port dedicated to it from 86 in 81, but does not appear to me, but it gives me an error page, because it recall the 86
example:
http://myserver:81/webroot/ becomes http://myserver:86/webroot/
I’ve checked .htaccess (but it’s void), all files in the webroot, in the database but nothing with 86
in wp-config.php there is this variable ABSPATH
where I can change it?
Can someone help me?

I’ve another similar error
inside of my lan, I can look the website that I development,but if I do the same outside of my lan the pages are without formatting only html without javascript and css
In my lan the address is similar to http://myserver:81/webroot/
and outside http://myserver.cjb.net:81/webroot/

bye and thanks for your help