Otto, I always take pictures, with my digital camera (macro setting), as I disassemble a carburetor.
It helps to refer to them during reassembly and it also helps to spot and record mistakes and modifications made by a previous rebuilder.
The accelerator pump assembly looks good to me. I don't have a diagram of a YF 684S but my YF 2100S has a tiny "pump stem retaining clip"
that fits into a notch on the pump stem. A real pain to install at times. I cannot see one in your pictures because the pump spring is hiding it.
It's possible that your model did not have one.
When you installed the new pump diaphragm did you put a little alcohol in the fuel bowl and operate the pump?
On the up stroke it should spit out a stream at the check ball and retaining clip (bottom of your picture #3).
When you finish the check, dump the alcohol and work the pump to get rid of the excess.
