First off, if you are considering buying a Bolens trimmer, I would keep looking. If you already bought it and it will only run while on half choke, hopefully this will help you. I started having issues after about a year of purchasing it. Starts ok and will run on half choke, but as soon as you fully back off the choke, it stalls.
On top of the carburetor there are two screws surrounded by an aluminum housing. They are partly flat on one side and the rest is round. Take a hack saw or dremel tool and start notching out the aluminum housing until you reach the top of the screws (be careful not to get any aluminum shavings inside the carburetor). Make a small notch in each screw until you can fit a small flat-head screwdriver in them. Rotate each screw 1/4 turn counter-clockwise. Now start it up and it should run great. If not, you have something else wrong.