Holley accelerator pump
m (→Pump shooters: minor clean up) |
m (→Pump shooters: minor clean up) |
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The pump cams having three screw positions can be used on a 50cc pump, in position #3. Some are only for use with a 50cc pump. | The pump cams having three screw positions can be used on a 50cc pump, in position #3. Some are only for use with a 50cc pump. | ||
| − | ===Pump shooters=== | + | ===Pump discharge nozzles, or "shooters"=== |
[[File:Brass and reg shooter views.jpg|thumb|400px|right|Brass tube type shooter on left, regular cast zinc shooter on right]] | [[File:Brass and reg shooter views.jpg|thumb|400px|right|Brass tube type shooter on left, regular cast zinc shooter on right]] | ||
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Larger diameter nozzles (0.035” - 0.037”) shorten the pump shot duration, but deliver a greater initial volume of fuel. These sizes should be used on applications where engine speed will increase rapidly (vehicles with good power-to-weight ratios). Best acceleration is achieved when the accelerator pump delivers the lean best power air/fuel ratio to the engine; not when the maximum volume of fuel is supplied. | Larger diameter nozzles (0.035” - 0.037”) shorten the pump shot duration, but deliver a greater initial volume of fuel. These sizes should be used on applications where engine speed will increase rapidly (vehicles with good power-to-weight ratios). Best acceleration is achieved when the accelerator pump delivers the lean best power air/fuel ratio to the engine; not when the maximum volume of fuel is supplied. | ||
| − | [[File:Hollow shooter.jpg|thumb|400px|left|"Hollow" screw]]If a shooter | + | [[File:Hollow shooter.jpg|thumb|400px|left|"Hollow" shooter screw]]If a shooter bigger than 0.038”-0.040” is required, a “hollow” shooter screw is advised. Above a 0.037” squirter size, a 50cc "REO" pump may also be required, available under Holley P/N 20-11. Make squirter changes in 3-step increments- i.e. if you have a 28, go to a 31, etc. |
Smaller sized accelerator pump squirters will cause the duration of the pump shot to be longer. Because the fuel cannot be compressed, the spring in the accelerator pump lever compresses then this spring pressure continues to supply fuel through the squirter until the spring has extended back to its original length. | Smaller sized accelerator pump squirters will cause the duration of the pump shot to be longer. Because the fuel cannot be compressed, the spring in the accelerator pump lever compresses then this spring pressure continues to supply fuel through the squirter until the spring has extended back to its original length. | ||
| − | An important point should be kept in mind when tuning a double pumper: The secondary accelerator pump must supply fuel for a sufficient time so that the secondary main nozzles can begin to flow fuel to the engine after the secondary throttles are opened. If the nozzles do not start by the time the pump shot expires, bogging will result. | + | An important point should be kept in mind when tuning a double pumper: The secondary accelerator pump must supply fuel for a sufficient time so that the secondary main nozzles can begin to flow fuel to the engine after the secondary throttles are opened. If the nozzles do not start by the time the pump shot expires, bogging will result. <br style="clear:both"/> |
Also check all used accelerator pump nozzles closely to see if they've been drilled oversize. If a shooter has been drilled out, the number on it obviously will no longer apply. You may have a hard time telling, if they did a good job so a numbered drill bit set or a wire spark plug gap feeler gauge will help determine the exact size. | Also check all used accelerator pump nozzles closely to see if they've been drilled oversize. If a shooter has been drilled out, the number on it obviously will no longer apply. You may have a hard time telling, if they did a good job so a numbered drill bit set or a wire spark plug gap feeler gauge will help determine the exact size. | ||
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