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techtalk:evo:carb06f [2019/08/27 15:31] hippysmack created |
techtalk:evo:carb06f [2024/01/02 22:32] (current) hippysmack |
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| ====== To Drill or Not to Drill the Keihin CV Carb Vacuum Slide Hole ====== | ====== To Drill or Not to Drill the Keihin CV Carb Vacuum Slide Hole ====== | ||
| - | Do not attempt to drill the slide. That usually causes more problems than it is worth. Put in a lighter spring if you want a faster response. ((XLXR of the XLFORUM http://xlforum.net/forums/showthread.php?t=1937640&page=3)) \\ | + | Do not attempt to drill the slide. That usually causes more problems than it is worth. Put in a lighter spring if you want a faster response. ((XLXR of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/180214-drilling-the-vacuum-slide/page3?t=1937640&page=3)) \\ |
| One of the main advantages of the CV carb is it avoids problems with the slide opening too quickly and starving the engine for fuel. | One of the main advantages of the CV carb is it avoids problems with the slide opening too quickly and starving the engine for fuel. | ||
| Drilling the vacuum slide hole is supposed to give you quicker throttle response. \\ | Drilling the vacuum slide hole is supposed to give you quicker throttle response. \\ | ||
| - | * As the larger port reduces air pressure above the diaphragm quicker, so the slide rises quicker. ((Folkie of the XLFORUM http://xlforum.net/forums/showthread.php?t=1937640&page=3)) \\ The problem is that it is easy to overdo it, and make the port too large. \\ This makes the slide rise too quickly, and possibly overshoot the proper position. \\ You can get the slide 'hunting' around, back and forth above and below the 'correct' position (ie: that which gives the required constant depression). | + | It's also the first thing the instructions say to do in a DynoJet kit. \\ |
| + | ("//Remove the vacuum slide from the carb. Remove the stock needle & spacers, noting the order of assembly. Locate the slide lift hole. With drill bit provided (DD #29) enlarge your slide lift hole//) \\ | ||
| + | * As the larger port reduces air pressure above the diaphragm quicker, so the slide rises quicker. ((Folkie of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/180214-drilling-the-vacuum-slide/page3?t=1937640&page=3)) \\ The problem is that it is easy to overdo it, and make the port too large. \\ This makes the slide rise too quickly, and possibly overshoot the proper position. \\ You can get the slide 'hunting' around, back and forth above and below the 'correct' position (ie: that which gives the required constant depression). | ||
| * The problem with making it too large, is that you can't make it smaller again. \\ If you end up with a too large hole, the only solution is to get a new slide and diaphragm. | * The problem with making it too large, is that you can't make it smaller again. \\ If you end up with a too large hole, the only solution is to get a new slide and diaphragm. | ||
| * Some of the jet kits come with a 1/8" drill, which is definitely too large. \\ The stock port is 0.097" in diameter. \\ What you are looking for, according to Buzz Buzzelli in the Harley-Davidson Sportster Performance Handbook, is a 20% - 25% increase in cross sectional area of the transfer port. \\ | * Some of the jet kits come with a 1/8" drill, which is definitely too large. \\ The stock port is 0.097" in diameter. \\ What you are looking for, according to Buzz Buzzelli in the Harley-Davidson Sportster Performance Handbook, is a 20% - 25% increase in cross sectional area of the transfer port. \\ | ||
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| But no doubt everyone you ask will give you a different answer. \\ | But no doubt everyone you ask will give you a different answer. \\ | ||
| - | This is from CV Performance on drilling the small hole in the slide: ((CVPerformance from the XLFORUM http://xlforum.net/forums/showthread.php?t=1937640&page=2)) | + | This is from CV Performance on drilling the small hole in the slide: ((CVPerformance from the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/180214-drilling-the-vacuum-slide/page2?t=1937640&page=2)) |
| <blockquote> \\ | <blockquote> \\ | ||
| When following our instructions that accompany our Tuners Kit, we only recommend the drilling with the supplied 7/64" bit as optional. \\ | When following our instructions that accompany our Tuners Kit, we only recommend the drilling with the supplied 7/64" bit as optional. \\ | ||
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| If you can wiggle it sideways a bit, the hole is too big. \\ | If you can wiggle it sideways a bit, the hole is too big. \\ | ||
| You can use an index drill bit kit to rod the hole with different size bits to be sure of the size. \\ | You can use an index drill bit kit to rod the hole with different size bits to be sure of the size. \\ | ||
| - | {{:techtalk:evo:carb:keihin_cv_vacuum_slide_comparison_by_matt_black_annotated.jpg?direct&300|}} ((photo by Matt Black of the XLFORUM, annotated by Hippysmack http://xlforum.net/forums/showthread.php?t=2068828&page=6)) {{:techtalk:ref:tools:pin_vise_1_by_hippysmack.jpg?direct&300|}} ((photo by Hippysmack)) \\ | + | {{:techtalk:evo:carb:keihin_cv_vacuum_slide_comparison_by_matt_black_annotated.jpg?direct&300|}} ((photo by Matt Black of the XLFORUM, annotated by Hippysmack https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/193103-newbie-cv-rebuild/page6?t=2068828&page=6)) {{:techtalk:ref:tools:pin_vise_1_by_hippysmack.jpg?direct&300|}} ((photo by Hippysmack)) \\ |
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