What you are feeling is exhaust which means the carburetor choke coil passage within the bottom of the manifold has been compromised. The hole in question will need to be plugged or the exhaust crossover passage blocked. If plugging the hole, then the hole on the bottom on the opposite side of the intake will likely also need plugging.
That hole and another one on the opposite side of the intake (which is likely on the bottom where you cannot see it) is suppose to be a simple passage going though the exhaust crossover but sealed to allow a vacuum source to pull heated air through the passage so the heat coil for an automatic choke can function properly. Because that passage way is leaking exhaust, either the intake casting or the pipe that goes through the exhaust crossover section is broken.
Two options at this point. Brokengate’s (Ted) suggestion of blocking the heat riser passage at the intake gasket is one. The other is plugging both ends of that holed passage at the intake. While you might get away with simply putting a threaded plug in the hole that’s leaking, I suspect you’ll find the exhaust still leaking at the other hole on the bottom of the intake. That one will require the intake to be removed.