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techtalk:evo:carb02 [2020/08/25 07:51]
ixl2relax [Internal Carb Checks]
techtalk:evo:carb02 [2020/10/30 21:31] (current)
ixl2relax
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 **Design Info** **Design Info**
  
-From 1989-later, the carburetor installed on Sportsters was made by Keihin. It has a 40mm maximum venturi, but the design of the constant-velocity carb utilizes a vacuum-operated slide to vary the venturi opening to help maintain a good air velocity throughout the carbs operating range.+From 1989-later, the carburetor installed on Sportsters was made by Keihin. It has a 40mm maximum venturi, but the design of the constant-velocity carb utilizes a vacuum-operated slide to vary the venturi opening to help maintain a proper ​air velocity throughout the carbs operating range.
  
-The CV40 uses a gravity-fed fuel supply through a float controlled inlet valve to fill a fuel supply bowl, from which the internal jets obtain fuel. It also has an enrichment system ​(mislabeled choke) that provides a pathway for fuel to bypass the carb and be supplied directly into the manifold for better starting.+The CV40 uses a gravity-fed fuel supply through a float controlled inlet valve to fill a fuel supply bowl, from which the internal jets obtain fuel. It also has an enrichment systemmislabeled ​choke. This provides a pathway for fuel to bypass ​most of the carb operation ​and be supplied directly into the manifold, at the rear of the carb, for better starting.
  
 There are a number of parts that operate in combination to control the mixing of fuel & air into a combustible fuel mixture. The vacuum slide, needle, main jet, slow jet, idle mixture screw, idle ports, tranfer ports and accelerator pump, all assist in this mixing operation over the range of operating conditions. There are a number of parts that operate in combination to control the mixing of fuel & air into a combustible fuel mixture. The vacuum slide, needle, main jet, slow jet, idle mixture screw, idle ports, tranfer ports and accelerator pump, all assist in this mixing operation over the range of operating conditions.
  
-The constant-velocity system provides a partial means of compensating for operation at different altitudes. In a fixed system, as altitude increases, the fuel mixture becomes richer due to the thinner air. But the CV system partially compensates for this fact because the vacuum-slide oparation is also affected by the thiner ​air, thereby supplying less fuel into the mix.+The purpose of the carburetor is to atomize fuel into the incoming air such that a proper air-fuel-ratio (AFR) is achieved for varying conditions. The Pilot & Main Jets each use an emulsion tube with a fuel orifice & air holes. Each emulsion tube pulls fuel from the float bowl reserve and is fed air thru small air ports (called air jets) on the face of the carb (filter side). In each case, the emulsion tube produces an air/fuel mixture that is further mixed with the air flowing into the venturi (carburetor throat). 
 + 
 +The air flow is generally controlled by the Throttle Plate along with the vertically moving slide that essentially varies the venturi size to create a Constant Velocity of air (from which it gets it's name). By selecting various Pilot and Main Jets, the AFR can be altered to produce a preferred ratio. Air flowing into the venturi creates a vacuum which pulls the air/fuel mixture from the emulsion tubes into the air stream. 
 + 
 +To create a proper idle operation, the Idle Port (on the engine side of the throttle plate) has a separate adjustable screw that allows some of the mixture from the Pilot Jet emulsion tube to be bled directly into the manifold, bypassing the throttle plate. 
 + 
 +As the throttle plate is opened, fuel is pulled from the Transfer Ports. With more throttle, fuel is pulled thru the needle jet, in greater quantity as the tapered needle is lifted out of the needle jet opening by the vacuum-operated slide. 
 + 
 +The constant-velocity system provides a partial means of compensating for operation at different altitudes. In a fixed system, as altitude increases, the fuel mixture becomes richer due to the thinner air. But the CV system partially compensates for this fact because the vacuum-slide oparation is also affected by the thinner ​air, thereby supplying less fuel into the mix.
  
 The CV40 (1989-later) has an accelerator pump, controlled by a rod attached to the throttle cable cam, to provide additional fuel when the throttle is quickly opened for acceleration. It squirts raw fuel into the venturi throat to enhance the fuel mixture along with the quickly added air. The CV40 (1989-later) has an accelerator pump, controlled by a rod attached to the throttle cable cam, to provide additional fuel when the throttle is quickly opened for acceleration. It squirts raw fuel into the venturi throat to enhance the fuel mixture along with the quickly added air.
  
-The carb has been adjusted to control exhaust emissions. The idle mixture is set at the factory and the adjusting screw is capped because it is not to be adjusted except by factory technicians.+The carb has been adjusted to control exhaust emissions. The idle mixture is set at the factory and the adjusting screw is capped because it is not to be adjusted except by factory technicians. The cap can be removed and adjustments can be made.
  
-Note from the service manual: Adjusting mixture setting by procedures other than specified in this section may be in violation of local regulations.+However, note this from the service manual ​(FYI): Adjusting mixture setting by procedures other than specified in this section may be in violation of local regulations.
  
 \\ \\
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 |Heads Installed |(Stock 883, Stock 1200, Specify Brand/​Model)| |Heads Installed |(Stock 883, Stock 1200, Specify Brand/​Model)|
 |Cam Installed |(Stock D, Stock W, Specify Brand/​Model)| |Cam Installed |(Stock D, Stock W, Specify Brand/​Model)|
-|Compression Test |( Min120PSI for 883 - Min150PSI for 1200 ) |+|Compression Test |( Min120PSI for 883 - Min150PSI ​for 1200 - 2004+ Min180PSI ​for 1200 ) |
 | | | | | |
 |Ignition Module |(Stock 883, Stock 1200, Specify Brand/​Model#​)| |Ignition Module |(Stock 883, Stock 1200, Specify Brand/​Model#​)|
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     * Be sure to reinstall pump rod correctly     * Be sure to reinstall pump rod correctly
   * Be sure you have removed each part, cleaned the ports & reinstalled correctly   * Be sure you have removed each part, cleaned the ports & reinstalled correctly
-  * Set the Idle Set Screw (located on the right side of the carb, near the throttle cables)\\ so that the Throttle Plate is between the Idle Port (one hole in the carb throat) and the\\ Transfer Ports (which consists of 5 holes nearby)+  * Set the Idle Set Screw (located on the right side of the carb, near the throttle cables)\\ so that the Throttle Plate is closed as much as possible. Try getting it between the Idle Port\\ (one hole in the carb throat) and the Transfer Ports (which consists of 5 holes nearby).\\ Don't obssess over it if you can't.
  
 \\ \\
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 (Using a 1/2-inch spacer to lift the float side of the carb will approximate the 15°-20° angle needed.)\\ (Using a 1/2-inch spacer to lift the float side of the carb will approximate the 15°-20° angle needed.)\\
-{{:​techtalk:​evo:​carb:​hd-cv40-floatlevel-instructions.jpg?​100|}}{{:​techtalk:​evo:​carb:​hd-cv40-floatlevel.jpg|}}\\ +{{:​techtalk:​evo:​carb:​hd-cv40-floatlevel-instructions.jpg?​250|}}{{:​techtalk:​evo:​carb:​hd-cv40-floatlevel.jpg|}}\\ 
-**Click on the small image above for the detailed instructions regarding setting the float level:**+**Click on the small image above for the detailed**\\ 
 +**instructions regarding setting the float level:**
  
 {{:​techtalk:​evo:​carb:​cv40-floatvalve-02.jpg?​300|}}{{:​techtalk:​evo:​carb:​cv40-floatvalve-01.jpg?​400|}} {{:​techtalk:​evo:​carb:​cv40-floatvalve-02.jpg?​300|}}{{:​techtalk:​evo:​carb:​cv40-floatvalve-01.jpg?​400|}}
  
 In [[http://​xlforum.net/​forums/​showthread.php?​t=2074492|This XLForum Thread]] there is a discussion of the float bowl overflowing and the possibility that it is caused by aftermarket float valves that are not of the proper design.((Images above by Hippysmack of the XLForum)) In [[http://​xlforum.net/​forums/​showthread.php?​t=2074492|This XLForum Thread]] there is a discussion of the float bowl overflowing and the possibility that it is caused by aftermarket float valves that are not of the proper design.((Images above by Hippysmack of the XLForum))
 +
 +** Tip for Inspecting Float Level - With Carb Installed **
 + 
 +HD advised of a tip for adjusting the float level thru Tech Tip #36 dated September 1993. \\
 +However, this only works if you have an overflow fitting on the bowl (carbs for 1200S models don't have this fitting). \\ 
 +  * Checking carburetor float level can be easily done without even removing the carburetor from the motorcycle.
 +  * Simply attach a section of clear model airplane fuel line to the float bowl overflow fitting.
 +  * A small diameter fuel line, which is compatible with gasoline, can be found in most hobby supply shops.
 +  * Route the hose upward alongside the carburetor body.
 +  * The motorcycle must be held level and be running to perform this test.
 +  * Open the float bowl drain screw and fuel will rise in the hose to the same level as that in the bowl itself.
 +  * In a carb with a properly adjusted float level the fuel level in this hose will be at the joint between the carb body and the float bowl face.
  
 \\ \\
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   * Check intake seals on manifold (at heads) - replace now while it's apart   * Check intake seals on manifold (at heads) - replace now while it's apart
   * Check intake seal between manifold & carb - replace now   * Check intake seal between manifold & carb - replace now
-  * Minimize Throttle Plate opening at idle - Set it between Idle Port & Transfer Ports [[http://​xlforum.net/​forums/​showthread.php?​t=1635658|(See this XLForum thread)]]+  * Minimize Throttle Plate opening at idle - Set it between Idle Port & Transfer Ports if possible ​[[http://​xlforum.net/​forums/​showthread.php?​t=1635658|(See this XLForum thread)]]
   * Check Idle Mixture Screw (IMS) screw/​spring/​washer/​o-ring condition - clean port   * Check Idle Mixture Screw (IMS) screw/​spring/​washer/​o-ring condition - clean port
   * 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 turns out from lite seat
- 
-==== Inspecting Float Level - Carb Installed ==== 
-  
-HD advised of a tip for adjusting the float level thru Tech Tip #36 dated September 1993. \\ 
-However, this only works if you have an overflow fitting on the bowl (carbs for 1200S models don't have this fitting). \\  
-  * Checking carburetor float level can be easily done without even removing the carburetor from the motorcycle. 
-  * Simply attach a section of clear model airplane fuel line to the float bowl overflow fitting. 
-  * Small diameter fuel line, which is compatible with gasoline, can be found in most hobby supply shops. 
-  * Route the hose upward alongside the carburetor body. The motorcycle must be held level and be running to perform this test. 
-  * Open the float bowl drain screw and fuel will rise in the tube to the same level as that in the bowl itself. 
-  * A carburetor with a properly adjusted float level will have the level the same height as the float bowl 0-ring surface. 
  
 \\ \\
 +
  
 ==== Change the Screws ==== ==== Change the Screws ====
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-**Throttle Plate** - To assure the throttle plate is capable of closing completely, back out the idle set screw (on the side of the carb near the throttle cable cam) so that it is not limiting the closing of the throttle plate.* Make sure the throttle plate rotates smoothly with the throttle cable cam. Set the position of the throttle plate, with the idle set screw, so that the bottom edge of the plate is closed just past the transfer port holes and is thus located between the single idle port hole and the multiple holes of the transfer ports. In practice, this is easier on some CV40 carbs than others. Do what you can to keep the plate as closed as possible, but don't obssess ​on getting it exactly between those port holes. Your viewing angle is skewed when looking in there, anyway.+**Throttle Plate** - To assure the throttle plate is capable of closing completely, back out the idle set screw (on the side of the carb near the throttle cable cam) so that it is not limiting the closing of the throttle plate.* Make sure the throttle plate rotates smoothly with the throttle cable cam. Set the position of the throttle plate, with the idle set screw, so that the bottom edge of the plate is closed ​as much as possible for setting the idle operation. Try getting it just past the transfer port holes and thus located between the single idle port hole and the multiple holes of the transfer ports. In practice, this is easier on some CV40 carbs than others. Do what you can to keep the plate as closed as possible, but DON'T OBSSESS ​on getting it exactly between those port holes. Your viewing angle is skewed when opening the throttle plate and looking in the venturi, anyway, so you see the hole before the plate is completely beyond it.
  
-(* If the throttle plate appears not to close fully with the idle screw fully wound out, carefully ​loosen the two throttle plate mounting screws, slightly. After the throttle plate is fully closed and has centered itself in the venturi, retighten the two mounting screws (don't overtighten & strip the threads). If by chance, for any reason, you have the throttle plate completely off, be aware that there is a right & wrong way to reinstall it. Be sure the plate is remounted with the right orientation because the top & bottom have an angled edge that needs to properly meet the carb venturi.)+(* It doesn'​t happen often, but if the throttle plate appears not to close fully with the idle screw fully wound out, it may need to be recentered in the throat. Carefully ​loosen the two throttle plate mounting screws, slightly. After the throttle plate is fully closed and has centered itself in the venturi, ​start to retighten the two mounting screws (don't overtighten & strip the threads) ​while opening & closing the throttle so the plate squares up with the shaft but also recenters in the venturi. If by chance, for any reason, you have the throttle plate completely off, be aware that there is a right & wrong way to reinstall it. Be sure the plate is remounted with the right orientation because the top & bottom have an angled edge that needs to properly meet the carb venturi.)
  
 {{ :​techtalk:​evo:​carb:​cv40-imscap-drillbit.jpg?​200|}} {{ :​techtalk:​evo:​carb:​cv40-imscap-drillbit.jpg?​200|}}
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 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 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.
  
-**Thus far,** the throttle plate has been positioned 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 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.
  
 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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-At this point, we need the engine to be warmed up to normal operating temperature to continue tuning the carb. A cold engine may operate quite differently once warmed up, therefore, tuning the carb while the engine is cold is not valid.+At this point, we need the engine to be warmed up to normal operating temperature to continue tuning the carb. A cold engine may operate quite differently once warmed up, therefore, tuning the carb while the engine is cold is not usually successful. 
 + 
 +Start the engine and use the enrichener (since the engine is cold) for the first 30-90 seconds, while you take the bike for a 10-15 minute ride to warm the engine fully. Then be careful of the burn potential while working around a hot engine and even hotter exhaust. Make sure you have no intake leaks in the manifold seals by using an unlit propane torch to flow propane around all three manifold seals. The engine idle will alter if an intake leak allows propane into the manifold.
  
-Start the engine and use the enrichener if the engine is cold, for the first minute or so, while you take the bike for a 10-15 minute ride to warm the engine fully. Then be careful of the burn potential while working around a hot engine. Make sure you have no intake leaks in the manifold seals by using an unlit propane torch to flow propane around those seals. The engine idle will alter if an intake leak allows propane into the manifold. 
  
 ==== The Idle Drop Method (IDM) ==== ==== The Idle Drop Method (IDM) ====
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 The Idle Drop Method (IDM) will help find the right setting for the Idle Mixture Screw (IMS)((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)((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.
  
-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 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 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).
  
 Now carefully reach under the carb and adjust the IMS with very small increments, turning it counter-clockwise (as if looking up from below). This is enrichening the fuel mix. Listen for the engine speed to begin faltering, then STOP adjusting the screw. Now begin turning the IMS clockwise with very small movements. Listen for the engine speed to return to running well and then begin faltering as you continue to turn the screw clockwise, which will create a lean condition. When it falters, STOP adjusting the screw. Now carefully reach under the carb and adjust the IMS with very small increments, turning it counter-clockwise (as if looking up from below). This is enrichening the fuel mix. Listen for the engine speed to begin faltering, then STOP adjusting the screw. Now begin turning the IMS clockwise with very small movements. Listen for the engine speed to return to running well and then begin faltering as you continue to turn the screw clockwise, which will create a lean condition. When it falters, STOP adjusting the screw.
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-**Once you have found the range,** use the counting you made (of the number of 1/8 turns) in order to make a setting of the IMS in the near center of the range you moved the screw from TOO RICH to TOO LEAN. For instance, if after finding the TOO RICH (CCW) setting, you then counted turning the screw SIX 1/8 turns (going CW) when you found the TOO LEAN condition, you would NOW turn the screw back (CCW) THREE 1/8 turns in order for it to be in the center of the range that operated well.+**Once you have found the range,** use the counting you made (of the number of 1/8 turns) in order to make a setting of the IMS in the near center of the range you moved the screw from TOO RICH to TOO LEAN. For instance, if after finding the TOO RICH (CCW) setting, you then counted turning the screw SIX 1/8 turns (going CW) when you found the TOO LEAN condition, you would NOW turn the screw back (CCW) THREE 1/8 turns in order for it to be in the center of the range that operated well. In fact, to be on the safe side of that setting, you  might want to go an extra 1/16 to 1/8 turn more rich.
  
 You can try this several times to assure yourself that you found the TOO RICH condition (CCW), then found the TOO LEAN condition (CW) and then were able to set the IMS (CCW) at the center between those. If the idle increases significantly during the adjustment, turn the throttle down to lower the RPMs and do the check again. You can try this several times to assure yourself that you found the TOO RICH condition (CCW), then found the TOO LEAN condition (CW) and then were able to set the IMS (CCW) at the center between those. If the idle increases significantly during the adjustment, turn the throttle down to lower the RPMs and do the check again.
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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.
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 ==== Other Engine Checks ==== ==== Other Engine Checks ====
-  * Check engine compression - Keep record for later comparison ​Preferred Minimum 883=120psi - 1200=150psi+  * Check engine compression - Keep record for later comparison 
 +    * Preferred Minimum883=120psi - 1200=150psi ​- 2004+ 1200=180psi
     * Warm up engine - Try a 10-15 minute ride - let engine cool just enough to touch     * Warm up engine - Try a 10-15 minute ride - let engine cool just enough to touch
     * Remove Spark Plugs & Air Cleaner - Connect gauge to Front Cylinder     * Remove Spark Plugs & Air Cleaner - Connect gauge to Front Cylinder
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 {{:​techtalk:​evo:​carb:​cv40-enrichener-assy.jpg|}}((Pics from Phillober t=848307\\ & gm1ll t=1553245))((Annotated by IXL2Relax at the XLForum)) {{:​techtalk:​evo:​carb:​cv40-enrichener-assy.jpg|}}((Pics from Phillober t=848307\\ & gm1ll t=1553245))((Annotated by IXL2Relax at the XLForum))
  
-An XLForum Thread ​showing ​the replacement of the cable is here: http://​xlforum.net/​forums/​showthread.php?​t=848307+An XLForum Thread ​discussing ​the replacement of the cable is here (but pics are missing): http://​xlforum.net/​forums/​showthread.php?​t=848307
  
 \\ \\
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 Reversion is created in the engine combustion cycle by the relationship between the cams and the exhaust system. Specifically,​ between the harmonic waves created in the exhaust pipes and the overlap of the exhaust valve about to close while the intake valve is already opening. This overlap period, where both valves are open at the same time, is usually extended in high lift cams, causing the exhaust system to have a great affect on the cylinder fill operation. The exhaust functioning can have a positive or negative affect. Reversion is created in the engine combustion cycle by the relationship between the cams and the exhaust system. Specifically,​ between the harmonic waves created in the exhaust pipes and the overlap of the exhaust valve about to close while the intake valve is already opening. This overlap period, where both valves are open at the same time, is usually extended in high lift cams, causing the exhaust system to have a great affect on the cylinder fill operation. The exhaust functioning can have a positive or negative affect.
  
-If/when reversion is occuring, the intake charge ends up passing through the carb three times: pulled in, pushed out, and pulled back in again. Each time it is picking up fuel making the mixture richer. ((Based on info from Aaron Wilson from the XLForum (aswracing) - http://​xlforum.net/​vbportal/​forums/​showthread.php?​t=1028905 - Post#12))+If/when reversion is occuring, the intake charge ends up passing through the carb three times: pulled in, pushed out, and pulled back in again. Each time it is picking up fuel making the mixture richer. ((Based on info from Aaron Wilson from the XLForum (aswracing) - http://​xlforum.net/​vbportal/​forums/​showthread.php?​t=1028905 - Post#15))
  
 You can read more in the REF Section on [[techtalk:​evo:​carb04#​exhaust_pipes_cams_-_power_or_reversion|Exhaust Pipes & Cams - Power or Reversion.]] ​ You can read more in the REF Section on [[techtalk:​evo:​carb04#​exhaust_pipes_cams_-_power_or_reversion|Exhaust Pipes & Cams - Power or Reversion.]] ​