First:
The bottom fitting on each carb is the fuel inlet nipple.
The top fitting is the fuel return nipple.
The middle fitting is the pulse nipple.
Typically, dual 38's run only one fuel pump on one carburetor. You can tell by looking at the square side of the carb - if one is bigger than the other carb, you have only one fuel pump. If they are both the same, you have two pumps. Another way to tell: If both carbs have pulse fittings, you have two pumps. One pulse fitting - only one pump.
Connect the pulse fitting(s) to the pulse fitting on the cases. If you have two fuel pumps and only one fitting on the cases, you can tee the lines or you can install another fitting.
Case 1 - Only one pump
The fuel line from the tank pickup runs to the fuel filter, then to the inlet nipple on the carb with the fuel pump.
Run a short hose from the outlet of carb 1 to the inlet of carb 2.
Then run the return line from the outlet of carb 2 back to the tank.
Case 2 - Two pumps
Run two fuel lines (use both pickups in the tank, make sure they are the same length tubes).
Run one filter per line.
Run each line into the inlet fitting on each carb.
Tee the return lines together.
