Purpose of 318 two-barrel Carburetor Base Gasket Notches?

[dibbons]

I don't believe the intake manifold has theses tiny notches/slots at the top and bottom in the photo. Well, when installed they would be on the left & right sides. I wonder what they do? I found at least one kit that also includes a gasket without the notches. Thank you.

 

[Vaanth]

I don't believe the intake manifold has theses tiny notches/slots at the top and bottom in the photo. Well, when installed they would be on the left & right sides. I wonder what they do? I found at least one kit that also includes a gasket without the notches. Thank you.

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The base gasket with slots for the Carter BBD 1-1/4 carburetor shown in the picture is for 1976 and prior models. The slots allow vacuum to be applied to the channels in the bottom of the throttle plate that connect to the choke pull-off and heated air inlet port feeds.

The throttle plate on the Carter BBD 1-1/4 was changed starting in 1977 to include the slots machined into the bottom of the throttle body itself. The gasket without slots is used for 1977 and later Carter BBD 1-1/4 caburetors.

The 1976 and earlier gasket with slots can be used on 1977 and later carburetors, but the 1977 gasket without slots cannot be used on 1976 and earlier carburetors because it will block the vacuum source to the channels in the bottom of the throttle plate.

The following images show the pages from the 1977 Service Highlights for more information about the carburetor and gasket changes: