The method's adaptability is one of its greatest strengths. The three tuning factors for part throttle are the size of the primary jet, the big and small diameters of the metering rod, and the power valve spring. Sometimes a simple spring adjustment can make a huge effect before we change the main metering jets or metering rods. On a little chart that we've given, we've listed the calibration starting points for when these springs begin to push the primary metering rod out of the main jet. The standard edelbrock avs2 calibration kit spring used in all Edelbrock carburetors is the 5 Hg or orange spring. Inches of mercury are used in this Hg specification, which also assesses manifold vacuum. When the pressure reaches 5 Hg, the spring will begin to push the power valve piston and lift the metering rod out of the primary jet. A buddy complained that his large car got rather poor fuel economy when driving at highway speed as an example of how this spring could be used to fine-tune a cruising condition. His 350ci small-block was getting less than 8 mpg at 75 mph.

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