The hole is a vent for the float chamber, but that carb has enough other issues I'm surprised Classic would ship something like that. The double gasket will interfere with the high speed mixture. (The carb will run rich) since it places the float and needle valve in the wrong position to work with the geometry of the drilled passages between the float chamber and the venturi. Return it for credit, and find some other supplier. Be sure to tell them why you're shopping elsewhere.
Jerry



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