I've been having this problem with my 66 mustang 289 summit 4brrl 600cfm auto trans. Pertronix with coil as well. Any help would be greatly appreciated, car turns on great responds well when accelerating thing is when I'm at a red light I notice the car start wanting to give out after a couple of seconds of just waiting on the light. spark plugs wiring set have been changed carb has been adjusted. If I give it gas it will respond as if nothing was wrong with the car. If I put it in neutral/park it will idle perfectly and if it's in gear and I put my foot on the brake and the other on the gas it responds well and won't hesitate to accelerate. Once again thanks in advance...