69 dart 225 1bbl...fuel dumping

I agree that a throttling valve will not work since the carb requires a widely varying flow rate between idle and WOT. It sounds like you are guessing on what the fuel level is when running. I think you can remove the economizer (3 screws on top) to see down into the fuel bowl when running. The most common cause of flooding is a bad needle or debris on the tip, however you tried a new carb. If too much pressure is forcing the needle open, you can fix w/ an in-line regulator. Most I have seen have a round knob with several settings, sold under many brand names. I have one on my 65 Dart currently. Some other types (3 port) require a return line to the fuel tank.