Originally posted by randywrench
The top secondary plate is spring loaded shut and when the lower plate opens air flow pulls the top open which controls extra fuel.Smog motors had a vacuum pull off to control when yhe secondarys could open(you don't need it!) The large port in the rear bottom threaded hole, orig was used for power brake vacuum it is supplying full vac. at idle. I put in a 1/4 inch pipe plug and put distributer vac. to the small port right next to the big one

that is what ive been trying to say for the last 20 min.