wont start mcculloch viginia mh555p?

This question was sent in another email I normally service all my own garden machines but the above machine was working but running very rich and rough so I tried to reset the petrol mix after cleaning air filter but now I have lost the setting and want the settings for carberator screwed totally in how many screws out is this the way to do it it works for lawn mowers Please give me a clue

James Gauld happywanerer@msn.com
February 2008