What's the timing set at? If it's so advanced that you cannot adjust the idle with the idle speed screw (you've got the screw all the way off the throttle shaft) snapping the throttle closed will do it. Try retarding the timing a bit, then giving it some idle screw to crack open the blades then see if the problem goes away. Or if you can't give back some timing, you may need to drill the idle air holes in the throttle blades bigger. When you blip the throttle and it kills, it's not getting enough air. A dash pot was the factory's answer to this, but not my choice, it's just another part to give you trouble later on..