Are you using the port to the rear of the carb? That is the right one. If so, your EGR valve, CTO switch, or cannister may be malfunctioning. Any of those could act like an open vacuum source making the motor die. If you are hooked up to the front port on the carb, it is a constant vacuum that will open the EGR when it should be closed--again making like a huge vacuum leak. That port is for vacuum advance on the distributor.