My Dad bought one of those a year ago and I borrowed it from him this year to cut .25 Acre Love it works great! You said the line was hitting the shroud which tells me your putting the line on wrong no offense intended. You should have the string divide in half per side of the 2 string head this one is a little different than the one I used it was Yard King or something from Sears and I had to pull the string through the eyelets and back over semi knot like the principle is the same hope this helps.
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=LAWN&fromAuto=YES&bidsite=CRAFT&pid=07177370000
http://www.murray.com/www/store/product.asp?mscssid=U98Q48UBXFF78K9DEB231QL22DD4DH75&pfid=TM5000X89A
I always like to buy enough line so that I have to buy new more often to keep it fresh I have heard of a few people during the Summer Months to keep it in a bucket of water to keep the resin from drying out can't speak for the best blades.