Turn the fuel divider rail upside down so the initial fuel feed from tank will come in from the top down to the pumps, instead of bottom up. That might help guarantee equal distribution to pumps. Also, take a good look at the carbs. If you are using the diaphragm style carbs, check the pop off pressure. They might need to be about 9 or more psi before they pop off releasing pressure, but check the Tillotson recommendations for those models to be sure if not known. If the pumps are exceeding the pop off pressure, then put stronger fuel "needle/seat closing springs" in to get them right.