Twenty Thirteen Right-Side Whitespace Issue on Mobile

I am having he same problem that several people seem to have but none of the solutions are working.

There is a wide whitespace on the right of the page when viewed on mobile devices.

I removed all of the custom CSS and this did not resolve it.

I’ve also read other blog posts that suggested these items:
.site-info
.site-footer .widget-area {
width: auto;
}
.norm_row.sfsi_wDiv {
width: auto !important;
}
.sfsi_Sicons .sf_fb .fb_iframe_widget > span {
width: auto !important;
}

The site is forum280.com. I would really appreciate the help.