Editing How to rebuild automotive carburetors
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==Introduction== | ==Introduction== | ||
Sooner or later, every hotrodder runs into the steps of making induction and carburetion choices while building a performance engine. | Sooner or later, every hotrodder runs into the steps of making induction and carburetion choices while building a performance engine. | ||
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It has been many years since a Holley carb (or ANY carb) has been used on a domestic production automobile, but regardless of that, the Holley carb will remain in use for many more years to come- of that there's little doubt. | It has been many years since a Holley carb (or ANY carb) has been used on a domestic production automobile, but regardless of that, the Holley carb will remain in use for many more years to come- of that there's little doubt. | ||
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[[File:Holley pv stamping1 id.jpg|thumb|left|400px| Holley power valve vacuum rating]] | [[File:Holley pv stamping1 id.jpg|thumb|left|400px| Holley power valve vacuum rating]] | ||
The Holley carb uses a power valve to supply additional fuel when the engine vacuum drops (and presumably the engine load increases). The amount of fuel it supplies is equal to about 7-8 jet numbers. If the rear power valve (if present) is removed, the threaded hole it was in has to be plugged. The jets have to be enlarged 7-8 jet sizes to compensate for the loss of fuel flow it provided. <br style="clear:both"/> | The Holley carb uses a power valve to supply additional fuel when the engine vacuum drops (and presumably the engine load increases). The amount of fuel it supplies is equal to about 7-8 jet numbers. If the rear power valve (if present) is removed, the threaded hole it was in has to be plugged. The jets have to be enlarged 7-8 jet sizes to compensate for the loss of fuel flow it provided. <br style="clear:both"/> | ||
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===Holley idle transfer slot=== | ===Holley idle transfer slot=== | ||
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): | 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): | ||
− | [[File:Holley | + | [[File:Holley transferslot.jpg]] <br style="clear:both"/> |
{{Note1}}Other carbs have similar transition circuits, and they need to have the throttle blades in the 'sweet spot' same as the Holley. If the throttle blades are open too far, a poor idle and off-idle transition can be the result. | {{Note1}}Other carbs have similar transition circuits, and they need to have the throttle blades in the 'sweet spot' same as the Holley. If the throttle blades are open too far, a poor idle and off-idle transition can be the result. | ||
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− | [[File:Oring holley sec.jpg|thumb | + | [[File:Oring holley sec.jpg|thumb|350px|Arrow indicates cork O-ring that seals the vacuum chamber to the main carb body]] |
Use a fresh cork O-ring to seal the secondary vacuum chamber assembly to the carb body. Using a light smear of Hylomar on the cork gasket helps it to seal and stay pliable. A small rubber O-ring may be used instead of the cork gasket to seal a Holley secondary chamber. If you try this, be sure the O-ring is sealing, w/o being ''too'' thick. | Use a fresh cork O-ring to seal the secondary vacuum chamber assembly to the carb body. Using a light smear of Hylomar on the cork gasket helps it to seal and stay pliable. A small rubber O-ring may be used instead of the cork gasket to seal a Holley secondary chamber. If you try this, be sure the O-ring is sealing, w/o being ''too'' thick. | ||
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− | + | Be sure the vacuum chamber is assembled correctly. The diaphragm can get misplaced/torn; if that happens there will be no secondaries. Also, the check ball can get left out or can stick or the check ball seat can be rough, allowing the secondaries to activate too easily. So be sure the check ball is present and the seat is well formed. | |
− | Be sure the vacuum chamber is assembled correctly. The diaphragm can | + | |
− | The seat can be re | + | The seat can be re formed by using an old check ball and a small punch. Drop the check ball into the check ball passage, then with the vacuum chamber solidly supported, lightly tap the old check ball with the punch and a small hammer. This re forms the seat. |
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− | '''NOTE:''' There are small | + | '''NOTE:''' There are small groove(S) in the vacuum chamber check ball seat. This is normal, so do not try to use this method to remove the grooves. They need to be there to allow the secondaries to work correctly. |
A tuning trick is to use a deeper or shallower groove to change the opening rate. A tool can be made from a modified phillips head screwdriver to cut deeper and/or more grooves in the seat. Also, a lighter (aluminum) check ball can be used. | A tuning trick is to use a deeper or shallower groove to change the opening rate. A tool can be made from a modified phillips head screwdriver to cut deeper and/or more grooves in the seat. Also, a lighter (aluminum) check ball can be used. | ||
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If you use your lips or a vacuum pump to pull a vacuum on the chamber (chamber off the carb), there should be some resistance felt; the diaphragm shouldn't be too easily retracted because the check ball should be restricting the vacuum somewhat. That tells you the check ball is there and is able to help modulate the secondary opening rate. | If you use your lips or a vacuum pump to pull a vacuum on the chamber (chamber off the carb), there should be some resistance felt; the diaphragm shouldn't be too easily retracted because the check ball should be restricting the vacuum somewhat. That tells you the check ball is there and is able to help modulate the secondary opening rate. | ||
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==Rochester Quadrajet carb== | ==Rochester Quadrajet carb== | ||
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===See also:=== | ===See also:=== | ||
*[[How to Rebuild a Rochester Quadrajet 4MV Carburetor]] | *[[How to Rebuild a Rochester Quadrajet 4MV Carburetor]] | ||
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===Quadrajet Tuning and Repair Parts=== | ===Quadrajet Tuning and Repair Parts=== | ||
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==Carter carb== | ==Carter carb== | ||
− | + | [http://www.mymopar.com/downloads/carterafbtuning.pdf Carter AFB Selection and Tuning Guidelines] from Federal Mogul | |
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[[Image:Thermoquad.jpg]] | [[Image:Thermoquad.jpg]] | ||
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[[Category:Carburetors]] | [[Category:Carburetors]] | ||
[[Category:Engine]] | [[Category:Engine]] | ||
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