I found this on the HotRod Network years ago and saved it. Check this out on your car.
The amount of fuel delivered by one accelerator-pump stroke is determined by the pump’s capacity and the profile of the pump cam. The time it takes for that fuel to be delivered is controlled by the pump-nozzle size. A larger pump nozzle delivers the fuel much sooner than a smaller pump nozzle. During acceleration tests, if you notice that the car first hesitates and then picks up, it’s a sure bet the pump-nozzle size should be increased. A backfire (lean condition) on acceleration also calls for a larger pump-nozzle size. Conversely, if off-idle acceleration does not feel crisp or clean, the pump-nozzle size may need to be decreased. Holley accelerator-pump nozzles are stamped with a number that indicates the drilled pump hole size. For example, apump nozzle stamped “35” has a 0.035-inch orifice. Pump nozzle sizes areavailable from 0.025 to 0.052 inch. Whenever a 0.040-inch or larger accelerator-pump nozzle is installed, the “hollow” pump-nozzle screw (PN26-12) should also be used. This screw allows extra fuel to flow to thepump nozzle, assuring that the pump nozzle itself will be the limiting restriction in the accelerator-pump fuel-supply system.
When changing the pump nozzle, it’s best to jump three sizes. For example, if there’s an offline hesitation with a No. 28 pump nozzle, try a No. 31 pump nozzle. If you must use a No. 37 (0.037-inch) or larger pump nozzle, then also use a 50cc pump. A 50cc accelerator-pump conversion kit is available under Holley PN 20-11 when maximum pump capacity is desired.
Once nozzle size has been selected, the accelerator-pump system can befurther tailored with the pump cam. Holley offers an assortment ofdifferent pump cams, each with uniquely different lift and durationprofiles that are available under Holley PN 20-12. The cam profileaffects the movement of the accelerator-pump lever and, subsequently,the amount of fuel delivered by the pump nozzle.