Choke pull-off (primary). Also known as a vacuum break. Used on some Quadrajet 4MV, 4 barrel carburetor.
The choke pulloff is used to open the choke valve slightly when starting cold.
This pull-off has two ports, one responds quickly with a hand pump pulling in and holding the stem easily. The other port has a check valve that causes it too pull in much slower, it will be difficult to test with a hand pump.