Each side of the carburetor has a separate and independent float system, consisting of a float chamber formed by a partition in the float bowl, a dual pontoon float, and a float needle valve and valve seat.
Fuel enters the carburetor through the fuel inlet in the primary side of the air horn. From this point fuel flows to the separate float chambers through a horizontal passage in the air horn. When the fuel reaches the prescribed level in ech float chamber, the float moves the needle valve against its seat to shut off the flow of fuel.
There is a fuel balance channel located in the side of the float bowl above normal fuel level which connects the fuel chambers on the primary and secondary sides. In this way, any abnormal rise in fuel level in one side of the carburetor bowl with automatically balance with the other side.
Both high and low float bowl designs are used in the Rochester 4-bore carburetors. The type used is dependent upon engine demans and underhood clearance. Boht round and "D" shaped float pontoons are used in the high float bowl. A smaller wedge shaped float is used in the low bowl design.
Float assist springs are used on some high bowl and all low bowl application. Their purpose is to assist the floats in holding the float needle valve closed, especially where fuel pressures are encountered.
The following types of float assemblies and assist springs are used:
A) See image above: A torsion spring wrapped around the float hinge pin with one end fastened to the float arm and the other end resting on the needle seat. This design is normally used with the high float bowl and the "D" shaped float.
B) See image below: A float balance spring is installed between the float hanger posts to apply pressure on the float tang at the rear of the float arm. The spring tension against the tang determines the float drop and will affect fuel level. With this type assist spring float drop setting is very critical.
C) See image below: A coiled spring located on the power piston stem exerts pressure on a tang on the float arm, whenever the power piston is in the up position. During heavy acceleration or power system operation, the power piston drops and releases all pressure applied to the tang. This allows maximum float drop under heavy fuel demands and assists in closing the needle under normal operation. With this system a vacuum assist spring adjustment is necessary.
Rochester 4 Jet, 4G, 4GC Float Level
Spring Loaded Floats - Torsion Spring
Some of the 4 Jet carburetors had a spring mounted on the float pin and hooked to the float. This helps take the bounce out of the float on rough roads. This is a part that is not being produced so what do we do now?
It is probably OK to leave them off; I do, however, reinstall them when I find that they are present. In the Era of Ethanol, carburetors can't have enough help!
That said, I have seen many come into the shop without them which, upon research, I found to have been originally so equipped. Since I had none to install, I simply left them off an they ran as well as any 4G is ever going to run.