I did a recipe job on my Buick carb and got a sucking sound and no idle.
After a lot of fruitles effort, I finally decided to remove the plywood open spacer and add a hard phenaulic 4 hole spacer.
My guess was that the carb was seeping air internally and the 4 hole spacer would support the bottom of the carb and sandwitch the gaskets with some squeeze from the bottom up. The carb had been unwarped, but there was possibily some sag in it somewhere until the 4 hole spacer gave it a solid foundation.