Cap, Figure it out, if fuel is leaking back past the flappers the pump isn't working right. The carb is ixhibiting multiple problems. The fork height was too high allowing fuel to flow back through the pump. And the pump diaphram is not seating correctly. The flappers act as check valves to control the direction of the fuel flow. The fuel flows from the tank to the pump to the metering diaphram. There is no provisions inside the carb to allow fuel to return to the tank if it is working correctly. The flappers work in conjunction with the pump diaphram. Unless the owner of the carb finds out why the fuel is flowing back through the pump he is going to have problems with his engine.
The metering needle will shut off fuel from flowing back to the carb and hide a faulty pump diaphram. Ki8FR should remove the metering needle, pump fuel to the carb then see if fuel flows back to the tank. If it doesn't flow back to the tank now perhaps he can say what fixes he did to the pump diaphram to fix it.
The meetering needle has one purpose, It opens and closes the flow from the pump to keep the fuel cavity full of gas.