what is this?

[Montehall]

I'm guessing its for a hot air choke, but the qjets have it built onto the carb
http://img.photobucket.com/albums/v257/Wilson1911/IMG_20130625_194329_098_zps7024c24b.jpg

[JRD77VET]

Correct, hot air choke. Just remove it if the carb has one.

[Fastguy]

There are two types of Q-jet choke housings. One has a linkage arm that runs to that coil spring and the other has a threaded outlet on the big circular housing that runs a tube into a plate that runs under the manifold.

[MrPeabody]

Fill that manifold with dirt and plant flowers in it.

[Montehall]

Fill that manifold with dirt and plant flowers in it.
Its better than nothing

[StaticCling]

You can get a block off plate for that if you run something other than a q jet. If you aren't replacing the manifold.....

[RED-85-Z51]

Why not use a...well, any other carb, other than a Qjet?

[Montehall]

Because there is absolutely nothing wrong with a properly setup quadrajet, and I happen to have one.