I can see no reason to not use the original mechanical pump. I would guess the electric pump is on there because the previous owner lost the mechanical pump. Eventuality the diaphragm rips open and the fuel pumps right into the crankcase.

I would hook it back up stock, with a filter between the pump and the carb. It is a great little fuel system. As the guy's here will tell you, the carbs on these things really don't run well with a lot of pressure.

Forget its a carb. Just think about it as a lot of small parts! There are some really good rebuilders out there. There is also some good help on You Tube.