The cover casting clearly has a provision for something (hot idle compensator, two-way bowl vent) that has not been installed. The tube looks homemade, same sharp edge on both ends as when you cut with a hand tool. The base plate doesn't have the canister vent tube for two-way bowl vent installed, if it was the hole through the base plate would connect it directly to manifold vacuum.
I'm not sure about that tube, I don't see the purpose of having it there. The hole drilled through the base plate makes no sense other than what Bewy suggested.
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