A good selection of accelerator pump discharge nozzle sizes is indispensable to the proper tuning of the accelerator pump system. The nozzle hole size determines the rate of fuel discharge. A larger hole will shoot the fuel at a faster rate, and with less pressure, than a smaller hole. Sizes are stamped on each nozzle. For example, the number 31 indicates that the nozzle hole size is .031- inches. Various styles of nozzles are offered by Holley.