I have an old Sears/Craftsman 9" - 3.5 hp edger trimmer model number 536.796536 with model number 143.754042 carburetor. It has become hard to start and when it does start it will only run with the choke half open. It dies when the choke is off. The fuel line is not blocked and adjusting the high speed idle does not help. Any suggestions before I take it to the repair shop?