These accelerator pumps are from a large bore Rochester 2G, liked you'd see on a Pontiac or Olds. The blue tone of the synthetic rubber cups identifies the material as Viton, a fluoropolymer elastomer made by DuPont. The two cups look and feel almost identical even though the one on the right is used and the other is brand new. It is highly resistant to the chemical effects of ethanol and other additives in pump gas. If you've been experiencing pump failure, installing a replacement featuring Viton could be your solution.