[Dan Case]

John is showing you, in the factory engine testing picture and his new pictures, are 48 IDM1 model carburetors. They are extremely rare and were not common in 1963.

Short course, a 46 mm IDM design was created as an upgrade from to the mid 1950s 45 IDM model. A few 46 IDM models were reworked into 48 IDM models for a Maserati Formula 1 effort. All this circa 1958-59. At this point my research leads to Ford Motor Company asking for a 48 mm unit for their sports and race car engine programs and the 48 IDM1 was created. There must not have been large numbers of 48 IDM1 marked units made based on ones I can account for decades ago or now. The 48 IDM5 replaced them as a general go to independent runner down draft carburetor for all kinds of race cars with all kinds of engines until the 48 IDA and 48 IDA1 both got to Shelby American circa late March or early April 1964. Not every race team or car abandoned the 48 IDM1 and 48 IDM5 models, at least not as soon as they could have and some never did. Shelby American used quite a few 48 IDM5 carburetors 1963-64.

The significant difference in design between 46 IDM, 46 IDM1, 48 IDM, and 48 IDM1 and the 48 IDM5 was in the throttle spindle support. The early units did not have ball bearings to support the throttle shafts. 48 IDM1 carburetors I have studied all had pressed in plain bronze bearings (a.k.a. bushings). The new 48 IDM5 (and the 46 IDM2) model used Conrad type radial contact ball bearings to support the spindle shaft and included the spring loaded leather bearing seals people are familiar with in several mid 1960s and later E. Weber carburetors.