The manifold vacuum is measured at the base of the carb or on the intake manifold somewhere. Don't tap into just one runner, though, as sometimes this will give funny readings. You need to check the signal that sees all the cylinders. Most Holley’s have a manifold vacuum port in the front on the passenger side under the primary float bowl. also plug any vacuum ports so that the only airflow is coming through the throttle bores alone. I remove the tape and check each port individually for all cylinders. On multiple carburetor intake manifolds, I will use two carb spacers just like the single carb. On a 3 x 2 intake, I tape the two end carb pads, and flow the center carb first.
Jun 03, 2020 · Does anybody know why an edelbrock carb would have a high idle? I've backed the screws all the way out and it idles at 1000 no lower. I was aiming for 900.-edelbrock 1406 600cfm-Manual choke-chevy 305-20 pounds of vacuum-6.2 psi of fuel-egr blocked all excess economy stuff deleted.