Chevrolet used a Zenith model O-4 on the 4 cylinder from 1915 through 1919.
The designation "O-4" is a model designation. During this period of time, very few carburetors had identifying numbers.
The "O" meant a Zenith type "O".
The "4" meant an S. A. E. standard size 1 mounting flange (center to center mounting of 2 3/8 or 2 7/16). Typically the size 1 would have a throttle bore of 1 3/6 ~ 1 3/8 depending on the efficiency of the carburetor.
The type O-4 was used on dozens of different applications (different throttle arms, different internal calibrations, different external linkage configurations). If you are looking for one, would suggest one of the carb gurus on here (JYD and Chipper come to mind), or try to find an original picture showing the external configuration for the 1916.
The biggest "gotcha" on these carbs are the floats. Pinholes may be repaired by someone who is VERY GOOD with an old-fashioned soldering iron (the square chunk of copper with a point that is heated by a blowtorch). Impossible to use an electric gun or a torch to repair the float. However, these floats also developed vertical fatigue cracks, which are above my paygrade to repair. The float has air inside; thus it may be tested by submerging in hot water. If there are issues, the leak will blow a stream of bubbles like an intertube with a nail.
Rebuilding kits, and other parts (other than floats) are available.
Jon.
Last edited by carbking; 01/10/19 09:59 AM.
