Have fitted home made float gasket to `65 Zenith. Now running very,very rich. What have i done wrong???

Is it the same carb as the later models? My 361v Zenith on the S3 has an o ring seal between the emulsion block (big lump screwed to the top cover) and the base. If you've made too thick a gasket it's probably stopping this from sealing properly and I think it will let fuel into the venturi. Try the proper gasket and a new o ring.