With the carb mounted on the engine, look into the venturi...If you can see the head of the screw with the throttle closed it's opening the wrong way....
the disc can be slightly out of position on the shaft...With the carb off the engine loosen the screw slightly and make sure the dimple is touching the shaft..You can wiggle the disc and shaft and get it to close completely, then tighten the screw..You should not be able to see any light around the disc when it's aligned correctly...The shaft is brass so don't try to break the screw when tightening it...Use a drop of Loctite on the screw if possible..You don't want the screw to come loose and go through the engine, it will destroy the cylinder and piston....