Hi Sledge, the "double pumper" refers to the accelerator pumps, with a single pump located on the primary side of the Holley in carbs with vacuum secondaries. A second accelerator pump can be found on the secondary (rear) side of the Holley when mechanical linkage is used. This is a picture of my 850 Holley double pumper, note the lack of vacuum linkage for the secondary side and the vertical spring and linkage just in front of the rear fuel connection which is the rear accelerator pump linkage - pumps in front and back = double pumper
