Correct Throttle Body Gasket
Installing the wrong gasket on a 4GC throttle body can make the carburetor act like it has a vacuum leak. It might run ok at higher RPM, but it will not idle properly, if at all.
Assuming your carburetor was running ok at one time, it would be safe to assume it has the correct gasket. Match it with the gasket from your carburetor kit.
There were a multitude of different accelerator pumps used on the 4GC carburetor. Hopefully you bought your kit, or will buy your carburetor kit using the carburetor number as a cross reference, not by going by the application. Still, you should be careful that you install the correct pump.
A pump that is too big in circumferance will bind and not allow the throttle to return to idle. A pump too small in circumferance will cause the carburetor to hesitate.
Make sure your accelerator pump return spring is returning the accelerator pump to it’s idle position.
Checking the Throttle Body
Did you remove the throttle plates? If so, then check for excessive gaps around the plates. Switching the plates, or turning them over could result in too much gap. Too much gap will make the carburetor hard to adjust for the idle speed. It may not idle down at all. This would be the same as stepping on the accelerator a little bit.