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techtalk:evo:carb02 [2020/08/30 03:01] ixl2relax [The Idle Drop Method (IDM)] |
techtalk:evo:carb02 [2020/08/30 03:03] ixl2relax [Carb Farts (coughing)] |
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| | When blipping the throttle, two things happen:\\ \\ 1. You are shooting some fuel in with the accelerator pump.\\ 2. When you blip the throttle, you are actually opening the throttle plate, and that larger opening causes a very [quick/temporary] minor drop in velocity through the carb and reduces the signal (vacuum, pull) across the fuel jets, so you flow less fuel for an instant. The accelerator pump is supposed to compensate for that somewhat. The problem is, with a very short stroke of the accelerator pump rod, like a blip does, not much if any fuel is actually shot, so the pump is not doing its job, in some cases. | | | When blipping the throttle, two things happen:\\ \\ 1. You are shooting some fuel in with the accelerator pump.\\ 2. When you blip the throttle, you are actually opening the throttle plate, and that larger opening causes a very [quick/temporary] minor drop in velocity through the carb and reduces the signal (vacuum, pull) across the fuel jets, so you flow less fuel for an instant. The accelerator pump is supposed to compensate for that somewhat. The problem is, with a very short stroke of the accelerator pump rod, like a blip does, not much if any fuel is actually shot, so the pump is not doing its job, in some cases. | | ||
| - | The second thing to say is that **YOU MUST** get a great tune from everything else before addressing the farts, because fixing other issues may eliminate or minimize the farts anyway. So, get your **timing** set correctly, get your **fuel flow** maximized and make certain you have no **air intake leaks.** Get your **throttle plate** set right (between idle & transfer ports), choose the right idle jet and use the Idle Drop Method to get the **Idle Mixture Screw** (IMS) set correctly. Make sure the bike is thoroughly warmed up before tuning. Each of these areas will need specific settings to match your engine build, whether stock, stage one, 1200/1250/1275 conversion, cams, etc. __BE SURE YOU READ ALL OF THE CARB TUNING INFORMATION IN THIS SECTION.__ | + | The second thing to say is that **YOU MUST** get a great tune from everything else before addressing the farts, because fixing other issues may eliminate or minimize the farts anyway. So, get your **timing** set correctly, get your **fuel flow** maximized and make certain you have no **air intake leaks.** Get your **throttle plate** set right (as much as possible between idle & transfer ports), choose the right idle jet and use the Idle Drop Method to get the **Idle Mixture Screw** (IMS) set correctly. Make sure the bike is thoroughly warmed up before tuning. Each of these areas will need specific settings to match your engine build, whether stock, stage one, 1200/1250/1275 conversion, cams, etc. __BE SURE YOU READ ALL OF THE CARB TUNING INFORMATION IN THIS SECTION.__ |
| The third thing to say is that it should be obvious that to correct a lean condition we need to add fuel to the mix (unless an air leak is the cause of the lean condition). But we need to add fuel carefully to address this quick, temporary, lean condition without drowning the entire carb operating range in extra fuel. A typical response is to increase the idle jet, but if you increase the idle jet larger than a size 45 or 46 you are flooding too much fuel into the transfer ports and the overall mix. | The third thing to say is that it should be obvious that to correct a lean condition we need to add fuel to the mix (unless an air leak is the cause of the lean condition). But we need to add fuel carefully to address this quick, temporary, lean condition without drowning the entire carb operating range in extra fuel. A typical response is to increase the idle jet, but if you increase the idle jet larger than a size 45 or 46 you are flooding too much fuel into the transfer ports and the overall mix. | ||
