An air bleed is the low end mixture control for your engine. It functions similar to a carburetor that has two needles, one for hi speed, and one for low speed. The biggest difference between a needle setting and an air bleed setting is the direction they are turned to achieve the desired results. In other words, to lean a two needle carb, you would turn turn the lo end clockwise to lean, and an air bleed screw would be turned counter clock wise to lean. When an air bleed is opened, the principle is more air, less fuel, therefore lean. Hope that helps_bob