I'm trying to find the same. As far as I can tell 50:1, or 2.6 oz. of 2 cycle oil to a gallon of gas (20cc per liter).
I got this from:
http://www.mymowerparts.com/pdf/Homelite_Service_and_repair_Manuals/HOMELITE%20STRING%20TRIMMER%20REPAIR%20MANUAL%20COVERS%20100%20DIFFERENT%20MODELS.pdf
J, August 2010