thats what I thought too, about the exhaust nipples. All four carbs sit on the plate and there are supposed to be t-connectors(which I dont have and would like to know where to get them) that attach to the intake nipples and split gasoline from one line. The intake nipples are only about an inch from each other and facing each other when the carbs are all on the plate.
I went out last night and blew air into the intake nipples and the air only comes out the hole at the top of the bowl section/bottom of the carb mechanism and not the float valve. The first two pictures will hopefully explain... on picture 12, the right pinhole leads to the intake nipple, the left pinhole leads to the exhaust nipple, and the float valve hole leads to a hole on the side of the carburetor, as seen on picture 13.