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| techtalk:evo:carb02 [2024/07/01 22:15] – [CV40 Needle, Jets & Idle Mixture Screw Parts] ixl2relax | techtalk:evo:carb02 [2024/07/01 22:27] (current) – [The Idle Drop Method (IDM) for Setting Idle Fuel] ixl2relax | ||
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| * Check Idle Mixture Screw (IMS) screw/ | * Check Idle Mixture Screw (IMS) screw/ | ||
| * Check IMS seat (Has the screw needle tip deformed the hole?) | * Check IMS seat (Has the screw needle tip deformed the hole?) | ||
| - | * Set initial IMS to 2-1/2 turns out from lite seat | + | * Set initial IMS to 2-1/2 full (360°) |
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| Because the richness of the fuel mix is controlled by the Slow Jet, which incorporates an emulsion tube to mix fuel & air, the size of the Slow Jet has a direct effect on the proper setting of the IMS. When the Slow Jet is enlarged, the IMS (& Transfer Ports) gets a richer mix and a lower number of turns open (on the IMS) will provide the same richness (as with the previous jet & larger IMS setting). | Because the richness of the fuel mix is controlled by the Slow Jet, which incorporates an emulsion tube to mix fuel & air, the size of the Slow Jet has a direct effect on the proper setting of the IMS. When the Slow Jet is enlarged, the IMS (& Transfer Ports) gets a richer mix and a lower number of turns open (on the IMS) will provide the same richness (as with the previous jet & larger IMS setting). | ||
| - | Having gained access to the IMS, it is recommended that you start by opening the IMS from GENTLY seated to 2-1/2 turns CCW. This setting is likely to be larger than the factory setting, which is often in the 1 to 1-1/2 turns range. By opening the IMS more, we are richening the Idle Fuel Mix to provide addition fuel during idle & transfer operations.This may also help the engine run cooler. | + | Having gained access to the IMS, it is recommended that you start by opening the IMS from GENTLY seated to 2-1/2 full (360°) |
| - | **Thus far,** the throttle plate has been positioned (as much as possible) between the Idle Port & the Transfer Ports, the Slow Jet has been chosen as stock or a 45 if the engine is 1200 or Stage One, the IMS cap was removed and the IMS was adjusted to 2-1/2 turns out from GENTLY seated. In addition, a selected needle was installed in the slide along with a reasonable choice for the Main Jet. These parts and settings were selected to provide a valid STARTING POINT for further, more accurate, adjustments. | + | **Thus far,** the throttle plate has been positioned (as much as possible) between the Idle Port & the Transfer Ports, the Slow Jet has been chosen as stock or a 45 if the engine is 1200 or Stage One, the IMS cap was removed and the IMS was adjusted to 2-1/2 full (360°) |
| While the proper idle rpm will be set AFTER adjusting the IMS setting (using the Idle Speed Screw), it is important to isolate the Idle Port operation from the Transfer Ports. | While the proper idle rpm will be set AFTER adjusting the IMS setting (using the Idle Speed Screw), it is important to isolate the Idle Port operation from the Transfer Ports. | ||
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| ==== The Idle Drop Method (IDM) for Setting Idle Fuel ==== | ==== The Idle Drop Method (IDM) for Setting Idle Fuel ==== | ||
| - | The Idle Drop Method (IDM) will help find the right setting for the Idle Mixture Screw (IMS) to supply the proper fuel mix to the Idle Port.((see the chrishajer thread link below)). At idle, the engine will have difficulty if the idle fuel mix is too lean or if the idle fuel mix is too rich. There is a small range between those excesses, which is the point of this adjustment. This procedure does require the correct Slow Jet, so you may need to change the Slow Jet if you cannot find the described idle range while performing the IDM. | + | The Idle Drop Method (IDM) will help find the right setting for the Idle Mixture Screw (IMS) to supply the proper fuel mix to the Idle Port.((see the chrishajer thread link below)). At idle, the engine will have difficulty if the idle fuel mix is too lean or if the idle fuel mix is too rich. There is a small range between those excesses, which is the point of this adjustment. This procedure does require the correct Slow Jet, so you may need to change the Slow Jet if you cannot find the described idle range while performing the IDM. Set the IMS initially to 2-1/2 full (360°) turns out from a lite seat (closed). |
| If you have previously set the throttle plate, between the idle port and the transfer ports, using the Idle Set Screw, you may need to roll the throttle slightly (at the beginning of this process) to keep the engine idle. With the throttle grip, set the idle speed as low as possible, yet still smooth engine operation. Lock the idle speed with the throttle grip lock (rather than changing the setting of the Idle Set Screw, which should still be (as close as possible) between the Idle Port & the Transfer Ports). | If you have previously set the throttle plate, between the idle port and the transfer ports, using the Idle Set Screw, you may need to roll the throttle slightly (at the beginning of this process) to keep the engine idle. With the throttle grip, set the idle speed as low as possible, yet still smooth engine operation. Lock the idle speed with the throttle grip lock (rather than changing the setting of the Idle Set Screw, which should still be (as close as possible) between the Idle Port & the Transfer Ports). | ||
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| - | | **Note - Trouble Finding A Change** - You may still have the throttle plate too far open, thereby running on the Transfer Ports instead of the Idle Port. But, if you have carefully set the throttle plate & still can't find a fall off until below 1/2 turn out, you need a smaller Slow Jet. If you can't find a fall off in idle until beyond 3-1/2 turns out, you need a larger Slow Jet. However, it is not recommended to use a smaller size than 42 nor larger size than 46. If the IMS setting appears to make no difference, you may have other issues. You may have an intake leak or exhaust leak. You may have fuel leaking into the carb thru the vacuum hose because of a defective petcock diaphragm or thru a defective Accelerator Pump diaphragm.((oldboy at Post#7 - https:// | + | | **Note - Trouble Finding A Change** - You may still have the throttle plate too far open, thereby running on the Transfer Ports instead of the Idle Port. But, if you have carefully set the throttle plate & still can't find a fall off until below 1/2 turn out, you need a smaller Slow Jet. If you can't find a fall off in idle until beyond 3-1/2 full (360°) |
