The return fuel line (if you don't have a regulator with a return fitting) is plugged where it goes to the tank, or you'll get fuel fumes out of it all the time. I still suspect that you are running too rich. What do the plugs look like now? Did you set the float height on the weber? Float adjustment does NOT like being shipped (dropped, banged around) and it could be way out, and if so, all mixtures will be off because extra or less vacuum is required to pull the fuel over the hill into the jet. The amount of manifold vacuum is what meters the fuel...

And, as I said before, if the fuel pump is overpressuring the float valve, especially at higher rpms, the float bowl will overflow into the carb barrel and you will be VERY rich. I would put an adjustable regulator into the fuel line from pump to carb, and temporarily lead the regulator return line into a clear container (Miller High Life bottle works nice) to see if a LOT of fuel is being bypassed, then hook the return up to the tank return line. You can usually SEE such a condition if it exists at idle by the fuel dripping in the throat of the carb (beware backfires and fried eyes). I hate carburetors...