var scrollSpeed = 125;
var step = 1;
var current = 0;
var imageWidth = 3800;
var headerWidth = 1900;
var restartPosition = -(imageWidth - headerWidth);
function scrollBg(){
	current -= step;
	if (current == restartPosition){
		current = 0;
	}
	$('.bg_main').css("background-position",current+"px 0");
}

var init = setInterval("scrollBg()", scrollSpeed);