Here it is here:
The accelerator pump system needs to counter the following two situations. So as not to discharge fuel through the squirters when the throttle is opened slowly, in some systems there is a controlled bleed from the pump back into the fuel bowl. Older carbs have a check valve located within the pump. When the throttle opening rates exceed a certain amount, the check valve closes and the fuel is redirected solely to the squirters. Also worthy of note is that some aftermarket Holley specialists drill a small bleed-back hole through the pump roof/float bowl floor. This hole needs to be small (about 0.012 inch), but it can be used as a tuning aid for the pump system in much the same way as Weber pump jet float bowl bleed-backs.
Good to see this in black and white,
.
Gary