Problems with Holley 1920

In the absence of a vacuum pump it is possible to pull the hose from the end of the choke pull-off, then depress the part that goes to the linkage towards the pull-off, then cap the end where the hose connected (vacuum port) with a finger. Release the linkage part, it should stay in, then go out when your finger is released from the vacuum port. This tests to see if a leak exists in the pull-off diaphragm.

If the pull-off tests good, and you did not replace the float in the carb rebuild it might be a gas logged. A defective float can dry out and run fine after a rebuild, then become gas soaked where it does not float, resulting in way too rich of mixture. Typically this happens in a few days.