2FastMoto reproduction Honda CB350F & CB400F round float bowl chamber rubber o-ring. The round o-ring must be hand fitted to the shape of the float bowl chamber gasket recess. Simply press it into the "house" shaped float bowl gasket recess at the top of the float bowl chamber. Then re-attach the float bowl chamber to the carburetor body, making sure the gasket is in alignment before completely tightening the float bowl chamber to the carburetor body.
Replacement from Honda carburetor gasket set: