WWhere did you get the new parts for the rebuild? Could the metering rod be incorrect?

Generic rebuild kits often have needle and seat sets that are not up to spec for the specific application but rather a part that "sort of works but not quite" for a variety of applications.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)