Holley 1920 diaphram return spring

That is a Holley 1920 for a 1968 225/automatic.

You should see solid shot of fuel squirting towards the middle from a hole in the inner wall of the carburetor, each and every time you operate the throttle lever with the engine off. If you do not, the accelerator pump has a problem. Not assembled correctly, missing parts, check balls not sealing. A faulty accelerator pump means you will get a stumble from a dead stop.