I pulled the 2v carb on this truck today..in hopes of rebuilding the carb. Looking down inside the manifold I see a threaded plughole..1" maybe....no plug in it and lower on the other side another plug hole maybe 3/4''. Anybody know what these are for and if they are supposed to have at one time had plugs in them? The carb has never been off the truck since 1978. TIA Jim