Jet and rod is changed to get the cruise air/fuel ratio leaned out
For altitude or high test fuel main metering jet can be replaced with leaner than standard metering jets
The Edelbrock Metering Jet is designed for use with the Edelbrock Performer Series and Thunder Series AVS carburetors. The jet and rod is changed to get the cruise air / fuel ratio leaned out. The step in the rod changes the effective jet area between high and low manifold vacuum conditions.