1/2" spacer on accelerator pump, what is it for?

[Cadman-iac]

  I've got this one accelerator pump that has this 1/2" tall spacer mounted above the spring and retainer and I've never seen one before. Unfortunately I didn't make note of which carburetor it came out of and I don't remember, it's been too many years. But it was unusual enough that I bagged it and saved it.
 The pump shaft is pretty long, and with the spacer on it it puts the pump seal way down in the well so whatever it was for it didn't have much of a pump shot.

 Does anyone know what the purpose of this spacer is?  I can post a picture tomorrow if necessary, I don't have one right now though.
 Thanks, just curious if I should save it or toss it.

[Kenth]

You can use it if you want to save fuel and lower emissions.

[Cadman-iac]

  I asked Cliff about it this morning when I added some stuff to my order, he wasn't sure either unless it was maybe from a 75 Cadillac carburetor, which I do have in my pile of cores. 
 

[Kenth]

As said, part of the smog era.

FWIW