If the carburetor top has a fuel inlet with pipe threads, then a adapter is needed for a flared line going to pipe thread. All fuel line should have a double flare on both ends. Adapters can be found at most NAPA stores and online. I can not think of any fuel line I have ever seen that didn't use a flared end. My local ACE hardware even carries the flare fitting adapters.

http://hosewarehouse.com/202x2-Male-Connector-Brass?gclid=CKXrsICBp8ACFQmAaQod-IsA7w

This is what you are looking for.

Joe