i have an Homelite XL 12 that dates from the 70 's . ?

There are three adjustments screws on it. Right next to the choke level ,there are two screws one above the other . Which one is the idle mix and the idle speed? And to the right of these two is another screw . What is it used for? What are the exact setting for each of these?Please help me ,I do not have the manual instruction any more.