Jet and rod sizes are always referred to by their diameter in thousands of an inch.
But fuel flow doesnt see diameters: The fuel sees the total metering area.
At WOT, the power valve unseats, and opens a fixed orifice, dumping a fixed amount of fuel in addition to the main jet. These rods have a fat diameter and a skinny diameter: The number stamped into the side of every metering rod is the fat diameter indicated in thousands of an inch.
The total metering area is 2.59 thousands of a square inch.
This is the metering area of this rod/jet combination with the rod fully inserted in the jet.
Rather, I will describe the various systems, their purpose, and a good tuning sequence to help you get each system and parameter set up correctly in the easiest way possible.
Quadra Jet carbs have three basic tuning variables, and these get people all confused: Primary Metering Jet, Primary Metering Rod, and Secondary Metering Rod.
It produces a lean operating condition for good fuel economy and good throttle response.
When engine vacuum is lost, indicating a high-power condition, the rods are pushed out of the jets by spring pressure, and only their skinny tips, or power tips, remain in the jets. All primary metering rods have the same power tip diameter (.026).
If the carb is a Carter manufactured under license froom Rochester, the number will be inside a round metal foil tag on the drivers side of the carb just above the primary throttle linkage.
Metering Area WOT fuel mixture is controlled only by the main jet size.
The Q-Jet is a highly versatile, tunable carb that will provide outstanding performance and reliability once set up correctly.