Holley accelerator pump
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The drawing below shows the transition slot as seen with the carb held upside down. The drawing on the left shows an overexposed transition slot. Baseline the throttle blades to give a transfer slot that looks like the image below, right (approximately as long as it is wide, or about 0.020", up to 0.040"): | The drawing below shows the transition slot as seen with the carb held upside down. The drawing on the left shows an overexposed transition slot. Baseline the throttle blades to give a transfer slot that looks like the image below, right (approximately as long as it is wide, or about 0.020", up to 0.040"): | ||
| − | [[File:Holley | + | [[File:Holley t-fer slot.jpg]] <br style="clear:both"/> |
From this point, if the idle speed is increased to the point where the transfer slot becomes over exposed, a poor idle and off-idle transition can be the result. One sure sign of this is the idle '''''mixture''''' screws do not cause the idle to change when turned in or out. Usually, adding initial timing to increase the idle speed will allow the throttle blades to be closed down some using the curb idle screw. This will return the idle mixture screws to normal and the idle will be smoother and cleaner, as will be the transition from idle to main circuits. | From this point, if the idle speed is increased to the point where the transfer slot becomes over exposed, a poor idle and off-idle transition can be the result. One sure sign of this is the idle '''''mixture''''' screws do not cause the idle to change when turned in or out. Usually, adding initial timing to increase the idle speed will allow the throttle blades to be closed down some using the curb idle screw. This will return the idle mixture screws to normal and the idle will be smoother and cleaner, as will be the transition from idle to main circuits. | ||
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[[File:Assembly.jpg]] | [[File:Assembly.jpg]] | ||
| − | Be sure the '''two''' gaskets are in place and not split. Any leakage past the gaskets will result in a less-than-normal discharge at the nozzles. | + | Be sure the '''two''' gaskets are in place and not split. Any leakage past the gaskets will result in a less-than-normal discharge at the nozzles. |
==Primary or secondary== | ==Primary or secondary== | ||
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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. | |
| − | The | + | 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. | |
| − | + | Only drill shooters oversize if it's absolutely necessary. For the best ''repeatable'' results use factory shooters. If you find you have to drill a shooter, no big deal, but do yourself a favor and etch the new size onto it so you'll know what it is later on. | |
| − | + | ||
| − | Only drill shooters oversize if it's absolutely necessary. | + | |
==Resources== | ==Resources== | ||
| − | *Holley's accelerator pump instructions are on [http://www.holley.com/data/Products/Technical/199R8108-2.pdf pages 6 and 7] | + | *[[Media:HolleyCarbList.pdf|Aftermarket Holley carb numerical listing]] by carb number |
| + | *[[Holley HP series carb specs]] by carb number | ||
| + | *Holley's accelerator pump instructions are on [http://www.holley.com/data/Products/Technical/199R8108-2.pdf pages 6 and 7] | ||
*[http://www.holley.com/TechService/Instructions.asp Holley instruction manuals by part number] | *[http://www.holley.com/TechService/Instructions.asp Holley instruction manuals by part number] | ||
*[http://www.holley.com/data/Products/Technical/199R10014.pdf Manual, Exploded View and Nomenclature]for Holley models 2010, 2300, 4010, 4011, 4150, 4160, 4165, 4175, and 4500 | *[http://www.holley.com/data/Products/Technical/199R10014.pdf Manual, Exploded View and Nomenclature]for Holley models 2010, 2300, 4010, 4011, 4150, 4160, 4165, 4175, and 4500 | ||
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