Only guessing, space it up for correct choke operation or an attempt to insulate carb from intake heat? I remember pitching the cluge and just running the thick gasket. I did a lot of stupid stuff back then.
The gaskets above and below the spacer are quite substantial, Almost like something you'd see on a fibrous exhaust manifold gasket with metal impregnated.
Probably asbestos so that's why I opted to stay away from scraping it clean to re-use.