IF your imagine is not shooting full Auto more than likely you are missing the jumper. Most retail stores remove this due to legal restraints on selling Automatic weapons.
All you need to do is go to a Radio Shack and pick up a pack of Jumpers.
http://www.radioshack.com/product/index.jsp?productId=2103807&cp=2032058&f=Taxonomy% 2FRSK%2F2032058&categoryId=2032058&kwCatId=2032058 &kw=jumpers&parentPage=search
Then on your board their will be 2 prongs sticking up that the jumper will fit on. Place the jumper securly over the prongs and you should be able to use full auto.