you have a serious internal carb problem if a half a turn on the mixture screw cause the car to stall at part throttle.your intermedate circuit is not flowing, when you go from idling circuit to the power circuit you must have no fuel flow.only other thing i have seen cause a problem simular to this is a leaky egr valve.when the valve opens just off idle it lean the intake charge out to much and stalls or bogs the engine.