[Steeveedee]

It's a new fuel pump, so I doubt that the poppets in it are leaking already. I suppose that that is possible, though. IIRC, the check valve at the filter is there in case the vehicle is upside down and fuel doesn't siphon out of the tank. Do you get a lot of black smoke when you have this condition? You could perform the same check for fuel inside the manifold as you did before with the other carburetor.