I don't know if you checked your tank as well, but along with checking for junk in the carb (my first guess), also check to make sure the clunk isn't stuck in your tank, or you don't have a hole in a fuel line inside or outside the tank. When the engine is running, do you see air bubbles in the line?

Also, some engines have issues with the o-rings on the high and low speed needles getting hard and/or shrinking. A bit of fuel tubing over the high speed needle to help seal it will often help.