Low speed is a jet located under the screw to adjust your idle , air bleed screw ( I believe thats what its called ) is the screw located close to the base of the carb , which I have been told 2 to 3 turns , but may depend on if those holes have been manipulated or not . The old rules I thought stated you couldn't remove the welch plug and work those 4 holes , but my understanding is that you can now , and have a no go gauge for them .