As we can see it's because your logo is too large and there is not enough space for the logo and menu items. So what you can do is center the logo between 850 and 1240px as you wrote above and this could be achieved with the following css:
@media only screen and (min-width: 850px) and (max-width: 1239px) { #Top_bar .logo { float: none !important; text-align: center !important width: 100% !important; } }
or decrease the padding between menu items:
@media only screen and (min-width: 850px) and (max-width: 1239px) { #Top_bar .menu > li > a span:not(.description) { padding: 0 !important; } }
Comments
we have an option for mobile logo and this could be set under Theme options > Responsive section.