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techtalk:evo:carb02 [2020/08/30 03:03]
ixl2relax [Carb Farts (coughing)]
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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 ==== 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.]] ​