Assuming that you have the high speed needle set correctly you need to adjust the "bleed" screw. It (the idle) is too rich. On this engine you need to back out the screw to open the bleed hole which will allow more air in. If the "bleed" opening is fully open then you MAY need to drill the "bleed" hole a LITTLE larger. Go real easy and don't make it too big. Also take the carb off the engine first.