65cc echo conversion, hda 16.6 mm carb. I can adjust the carb for a good top end and smooth idle. From idle up to about 1/2 throttle it runs rich. I can not adjust he mixture screws for a smooth midrange and full speed/ decent idle, it goes lean , top and bottom end, with a smooth midrange. I bent the pop off lever to meter less fuel. Bend it more? Is the carb too big? It runs real smooth with a smaller carb but the top end looses 500+ RPM. It is making good top end power spinning a MENS 22x10 at 7000. The plug shows a rich mixture. I am running mid grade gasoline.