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techtalk:ih:carb01r [2020/08/03 23:45] hippysmack [Keihin Butterfly Carb (non CV) Functions, Adjustments, Tuning] |
techtalk:ih:carb01r [2023/12/29 21:29] hippysmack |
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| - A good rebuild kit (new rubbers all through a carb make a big difference to it's performance) | - A good rebuild kit (new rubbers all through a carb make a big difference to it's performance) | ||
| - | The L76-78 Keihin butterfly carbs worked the best and had more adjustment to them. ((oldnavy of the XLFORUM http://xlforum.net/forums/showthread.php?t=877868&page=2)) \\ | + | The L76-78 Keihin butterfly carbs worked the best and had more adjustment to them. ((oldnavy of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/101363-keihin-butterfly-accelerator-adjustments/page2?t=877868&page=2)) \\ |
| They had no choke cam, a deeper frost plug in the top and a wider range in them. \\ | They had no choke cam, a deeper frost plug in the top and a wider range in them. \\ | ||
| Another factory fix was to seal the frost plug in the top with silicone to be sure they weren't leaking. \\ | Another factory fix was to seal the frost plug in the top with silicone to be sure they weren't leaking. \\ | ||
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| See which best fits the most narrow part (throat) of the venturi. \\ | See which best fits the most narrow part (throat) of the venturi. \\ | ||
| - | {{:techtalk:ih:carb:keihin_buttefly_ac_side_functions_by_spuggy_-_annotated_by_hippysmack.jpg?direct&300|}} ((photo by spuggy of the XLFORUM, annotated by Hippysmack http://xlforum.net/forums/showthread.php?p=5694195&highlight=keihin#post5694195)) | + | {{:techtalk:ih:carb:keihin_buttefly_ac_side_functions_by_spuggy_-_annotated_by_hippysmack.jpg?direct&300|}} ((photo by spuggy of the XLFORUM, annotated by Hippysmack https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/194516-choices-choices-what-carb-for-69-xlch?highlight=keihin#post4226385)) |
| ====== Choke ====== | ====== Choke ====== | ||
| - | |||
| On L76-78 Keihin carbs, the choke system is standalone with a choke plate and an actuating rod. \\ | On L76-78 Keihin carbs, the choke system is standalone with a choke plate and an actuating rod. \\ | ||
| On 79-up carbs, the choke system is composed of a choke, actuating rod and a fast idle cam. \\ | On 79-up carbs, the choke system is composed of a choke, actuating rod and a fast idle cam. \\ | ||
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| - Fully open (off for normal operating temp). | - Fully open (off for normal operating temp). | ||
| **79-87 models**: \\ | **79-87 models**: \\ | ||
| - | The choke has 4 basic positions ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=1383309&page=2)) \\ | + | The choke has 4 basic positions ((IronMick of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/130833-keihin-fast-idle-pilot-screw-adjust/page2?t=1383309&page=2)) \\ |
| - Full choke for cold startup (knob all the way in). | - Full choke for cold startup (knob all the way in). | ||
| - Choke out a little (maybe 1/2"). \\ (choke plate is still fully open but the fast idle cam moves the throttle valve to the fast idle position) | - Choke out a little (maybe 1/2"). \\ (choke plate is still fully open but the fast idle cam moves the throttle valve to the fast idle position) | ||
| Line 46: | Line 44: | ||
| - Choke all the way out, plate is fully closed and valve is in the highest idle position | - Choke all the way out, plate is fully closed and valve is in the highest idle position | ||
| - | Check your butterfly shaft also. If its loose, the bushings are worn and you'll be sucking air. ((egarrett of the XLFORUM http://xlforum.net/forums/showthread.php?t=575622&page=2)) \\ | + | Check your butterfly shaft also. If its loose, the bushings are worn and you'll be sucking air. ((egarrett of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/79254-missing-carb-parts/page2?t=575622&page=2)) \\ |
| ====== Low Speed System (idle circuit) ====== | ====== Low Speed System (idle circuit) ====== | ||
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| - Adjust idle SPEED screw again to get desired idle speed. | - Adjust idle SPEED screw again to get desired idle speed. | ||
| - | **Observations from Hopper of the XLFORUM**: ((http://xlforum.net/forums/showthread.php?t=276157&page=2)) \\ | + | **Observations from Hopper of the XLFORUM**: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/55576-how-to-tune-keihin-carbs-links/page2?t=276157&page=2)) \\ |
| <blockquote>I have found that the spring on the idle speed screw tends to creep the idle speed back up if you try to adjust the idle just that little bit slower. \\ | <blockquote>I have found that the spring on the idle speed screw tends to creep the idle speed back up if you try to adjust the idle just that little bit slower. \\ | ||
| Line 82: | Line 80: | ||
| **Further explanation from IronMick of the XLFORUM**; \\ | **Further explanation from IronMick of the XLFORUM**; \\ | ||
| - | <blockquote>If the carb is old and dirty the pilot screw passage may be gummed up such that you will not be able to "gently seat" the pilot screw reliably. ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=71361)) \\ | + | <blockquote>If the carb is old and dirty the pilot screw passage may be gummed up such that you will not be able to "gently seat" the pilot screw reliably. ((IronMick of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/36692-setting-the-pilot-screw-on-your-ironhead?t=71361)) \\ |
| If this is the case remove the carb from the bike and clean it up. Some guys try to do carb work with the carb in the bike. This is generally a very bad idea. \\ | If this is the case remove the carb from the bike and clean it up. Some guys try to do carb work with the carb in the bike. This is generally a very bad idea. \\ | ||
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| The screw usually comes out easily. The other parts may require some work. \\ | The screw usually comes out easily. The other parts may require some work. \\ | ||
| The best technique is to stick a pipe cleaner in the hole, twist it around, and, like magic, out come the other parts on the end of the pipe cleaner. \\ | The best technique is to stick a pipe cleaner in the hole, twist it around, and, like magic, out come the other parts on the end of the pipe cleaner. \\ | ||
| - | * The pilot screw adjustment mainly affects the idle speed operation of the engine. ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=71361)) \\ This is when the engine is actually idling, and when you release the throttle while riding. \\ If the pilot screw is too lean you get backfire in the exhaust when you throttle down, and white looking spark plugs. \\ If it is too rich you get black sooty exhaust and black sooty spark plugs. \\ Either situation has serious consequences for engine longevity if left unresolved. | + | * The pilot screw adjustment mainly affects the idle speed operation of the engine. ((IronMick of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/36692-setting-the-pilot-screw-on-your-ironhead?t=71361)) \\ This is when the engine is actually idling, and when you release the throttle while riding. \\ If the pilot screw is too lean you get backfire in the exhaust when you throttle down, and white looking spark plugs. \\ If it is too rich you get black sooty exhaust and black sooty spark plugs. \\ Either situation has serious consequences for engine longevity if left unresolved. |
| The mixture screw does not have a large range of adjustment, if you're running lean, you may need to increase the low speed jet size. \\ (after you have eliminated all other contributing factors) \\ | The mixture screw does not have a large range of adjustment, if you're running lean, you may need to increase the low speed jet size. \\ (after you have eliminated all other contributing factors) \\ | ||
| **Note**: 1966 to 1978 Sportster carbs do not have the O-ring and washer in the pilot screw passage. | **Note**: 1966 to 1978 Sportster carbs do not have the O-ring and washer in the pilot screw passage. | ||
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| </blockquote> | </blockquote> | ||
| - | |||
| ===== Air/Fuel Mixture Adjustment ===== | ===== Air/Fuel Mixture Adjustment ===== | ||
| - | |||
| **Low speed / idle mixture screw**: \\ | **Low speed / idle mixture screw**: \\ | ||
| - | Other names include the idle mixture screw or the pilot screw. ((IronMick of the XLFORUM http://xlforum.net/forums/showthread.php?t=1383309&page=3)) \\ | + | Other names include the idle mixture screw or the pilot screw. ((IronMick of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/130833-keihin-fast-idle-pilot-screw-adjust/page3?t=1383309&page=3)) \\ |
| - | You may get smoother running by adjusting this screw as it adjusts the flow of gasoline at idle. ((Hopper of the XLFORUM http://xlforum.net/forums/showthread.php?t=1383309&page=3)) \\ | + | You may get smoother running by adjusting this screw as it adjusts the flow of gasoline at idle. ((Hopper of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/130833-keihin-fast-idle-pilot-screw-adjust/page3?t=1383309&page=3)) \\ |
| The idle mixture screw is held in place by a spring on top of the carburetor near the intake mounting flange on all models. \\ | The idle mixture screw is held in place by a spring on top of the carburetor near the intake mounting flange on all models. \\ | ||
