The best method to calibrate the wide-open jetting is on a chassis dyno, but lacking that, a stopwatch or the seat-of-the-pants approach will work. And while it's seldom required, if wide-open throttle recalibration is necessary, Edelbrock suggests the following procedure:
* Select an rpm range to use in evaluating the WOT power. As a rule, use the highest 50 percent of the real powerband. If your engine makes good power up to 5,000 rpm, then 2,500-5,000 is a good range. If peak power is at 6,500 rpm, then 3,500-6,500 would be a good pick. Be sure not to select rpm higher than the engine's useful powerband.
* Accelerate at WOT from 1,000 rpm below the range you have elected to a few hundred over the range. Time the acceleration with a stopwatch. Be sure to time only the interval while the engine is sweeping through the selected range. Make enough timed accelerations to get a good average that is not affected by wind or grade.
* Refer to the calibration reference chart for your model (in the owners manual or with the calibration kit). Find the richest primary metering power mode change that can be made without changing a jet; it will probably be two stages (eight percent) richer.
* Change to the indicated rods, test again, and compare the times. Do not be surprised if there is no difference.
Compare the results of timed acceleration on this run to the base calibration and refer to the following section that best describes your situation:
* Faster than base calibration, change secondaries, go two stages richer, and perform acceleration test #3. If test #3 is the same as #2, you're done. Slower, change to one stage richer for the primary and secondary and you're done.
* If test #3 is still faster than #2, go three stages richer for the primary and secondary and keep going richer until there is no change (or slower) in the times. Stay at the first "no change" level, so that you remain within the richer of any two levels of calibration that have the same power.
If the preceding changes result in slower times:
* Go to one stage lean on the primaries, one stage lean on the secondaries, and perform another acceleration test. If test time is the same as base calibration, go back to the base calibration. If it's faster than base calibration, go to two stages lean on both the primaries and the secondaries. Keep going in the lean direction until there is no change or slower, then back up one stage richer so that you stay with the richer of any two levels of calibration that have the same power.
If these changes provide the same results, go back to the base calibration.
Here is a vacuum piston, metering...
Here is a vacuum piston, metering rod, and jet. Note the end of the metering rod is tapered and has two distinct diameters. All metering rods have an identification number that indicates the diameters of each portion.
Screws retain the covers over...
Screws retain the covers over the metering rod/piston/spring assemblies; they're located next to the choke between the primary and secondary venturis.
Swapping metering rods is...
Swapping metering rods is simple and quick, making the Performer one of the easiest of all carburetors to tune.