bolling
With respect, that is not how I showed it. Schroll back to my message. I also had both types of carbs here 77 and 78. I had one like you have apparently two of, with the return spring on the large shaft and the other (which for me was on the 77 bike), had the return spring near the throttle speed adjustment as toytuff has now. Question for you: do one or both of your PD carbs have a plastic breather canister on a short length of rubber hose attached to a vent port in about the center of the carb assy? This for me was the 78. My 78 had this and the return springs as you have them. Curiously, the fiche at servicehonda.com shows for 77 and 78 the type of return spring that toytuff has and not the type that you and I have and it does not show the breather for 78. So Honda documentation is apparently not perfect.
Toytuff - I think the rubber foam is to be stuffed inside the spring, down the hole in the center. I am not sure, but I believe that it provides damping, like a shock absorber, to reduce vibration.
Just clip the spring into the holes I showed on your picture (and you have shown) and you are all set. No need to remove the #4 carb as Bolling suggested because he was thinking I believe of the other type of return spring.
Good luck!