My brother just bought a 78 ford with a 400m the motor has been rebuilt. It has a vacuum leak that i cant get to stop underneath the carb on the drivers side. i have tried 3 different carbs and the all leak at the same spot when i spray starting fluid it revs up at the same spot everytime, on all 3 carbs. i know the other carbs are good, i took them off my other daily drivers. it has a 1/8" plate sandwiched between 2 gaskets, what is it for? it has a performer intake with an edelbrock carb. anyone have any ideas?