Might sell the tool. I have seen some that are half moons and others that are splined 12+ points like a torx.
I just used a thin grinding disc on a dremel and cut a slot so I could adjust it with a flat screwdriver.
I couldn't get either carb to work so I scrapped the machine.
One thing you should check is the exhaust. Remove the muffler and see if it runs properly. There is a spark arrestor screen that will get clogged with carbon. Either remove it or clean it.