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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Often the best place to start is to baseline the carb back to factory specs. This eliminates any chance that a previous owner's changes will mess up the way the carb works on your engine. | Often the best place to start is to baseline the carb back to factory specs. This eliminates any chance that a previous owner's changes will mess up the way the carb works on your engine. | ||
− | + | [http://www.usmotors.cz/old/tech_tips/HolleyCarbList.pdf '''Holley Carb Numerical Listing'''] is a list that shows the factory settings as well as the part numbers for rebuild kits and gaskets. To compare metering plates to jet sizes, see [http://www.holley.com/data/Catalogs/Holley/90.pdf '''Metering-Plate-to-Main-Jet Correlation Chart''']. | |
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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): | 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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