Diaphragm carbs on gassers are not set the same way as 2-needle glow carbs. The low needle on a gasser effects the carb mixture from idle to full throttle. The high needle effects the carb mixture from about half throttle to full throttle. With a gasser, you set the low needle first for good idle and responsive acceleration to about one third throttle when you snap the throttle open from idle quickly. Once you have the low needle set, adjust the high needle to max rpm with a tach, and back the needle open a little to make sure the mixture is slightly rich (down 100 rpm from peak). Test fly. If it sags or slows down on vertical lines, richen the high needle about 1/8th turn and try again.