Help me George? Please?

I've been having some problems with a vacuum leak, but I think I fixed it. Don't know how, but it's running fine now.
But while cleaning up everything and comparing my carbs to the carbs shown in my Clymers, I noticed my vacuum sensor is missing. The one on #2 carb, right next to the accelerator pump. There's the diaphram hole and three empty screw holes around it. What does that sensor do, and since it seems to be running fine, do I need it? Was this sensor only used on certain models, and my B4 didn't need it? There doesn't seem to be a vacuum leak there. I sprayed WD-40 up into it while it was running and it didn't speed up or anything.

Your LTD wasn't fitted with the cover that appears to be missing. There is a small passageway from the other diaphragm area to the area where the missing cover is located. On your assembly, there is a BB type ball pressed into the hole that effectively blocks this function off. On some of the VM26 accelerator pump assemblies, this bottom part was used and a cover fitted and all the VM24 w/pump assemblies used it. You can double check by looking for the pressed in BB... it will be about 1/4" away from the very center of the casting.

Thank you very much George. Been driving me crazy.