I have a stock, original 69 Mach 1 - 351W, 4bbl. The carb is the factory 4300 rebuilt several years ago long before I bought the car. I have no vac. on idle at the dist. port. On all the other mustangs/fords I've had over the years I've always had vac at idle and when you set the timing you unhook and plug the vac line to the dist. Does anyone have any ideas. Other than this my 83K mi. car runs great.