What is condition of the fuel tank? Here I have had problems with these carburetors when the tanks are rusty or had old fuel left in them causing the fuel pickup screens to clog during carburetor rebuilds. Sometimes the only solution is a new tank and re-cleaning the carburetor assembly.
The fuel gasket on this setup is there to prevent fuel leaks primarily using sealant is not necessary unless the gasket is damage but that can problems in itself.
