while engine is running place hand over top of carb. as if to choke it...if dies no vac. leak in carb....
if it idles up you got vacuum leak....note: do it slowley... as to pull a vac with hand....don't forget to check the vacuum mod. line on trans. pull line off .see if fluid is present..if so replace...check hose for cracks....
also ,might be vacuum booster let sit over night,,
pull off hose check for vacuum..if non replace..
if all thats ok...take carb.cleaner spray around while running to check for vacuum leak......mark