css like this
#header{
    background:url(/img/bg-clouds.png)  scroll 0px -40px;
}          
javascript code:
$( function($) {
    var current = 0;
setInterval(function(){
   if(current==-2240) {current=0;}
   current -=224;
   $('#header').animate({backgroundPosition:current+"px -40px"},2500);
},2500);
})