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--- tecnica:motori:keihin_cv_carburetor [2026/04/10 09:38] – created niccolo
+++ tecnica:motori:keihin_cv_carburetor [2026/04/12 10:35] (current) – niccolo
@@ Line 1: / Line 1: @@
 ====== The Keihin CV carburetor ======
+{{ .:keihin:honda-ntv650-keihin-carburetor-code.jpg?direct&200|}}
+Here some details about the carburetors mounted on the Honda NTV 650 Revere. They are two Keihin carburetors marked as **G4AACDt**. They are constant velocity (CV) carburetors, that uses engine vacuum to operate a diaphragm-controlled slide, rather than a direct cable connection.
+===== Nomenclature =====
+  * Jet needle
+  * Main jet
+  * Needle jet
+  * Slow jet
+  * Pilot screw
+  * Float valve
+  * Choke valve
+  * Air cut off valve
+**NOTICE**: The terms **slow**, **idle**, and **pilot** are used more or less interchangeably in Honda manuals and Keihin carburetor documentation.
+{{.:keihin:keihin-side-view.jpg?180|}}
+{{.:keihin:keihin-float-chamber.jpg?180|}}
+{{.:keihin:keihin-vacuum-chamber.jpg?180|}}
+{{.:keihin:keihin-airbox-view.jpg?180|}}
+{{.:keihin:keihin-engine-view-bottom.jpg?180|}}
+{{.:keihin:keihin-engine-view-top.jpg?180|}}
+{{.:keihin:keihin-air-cut-off.jpg?180|}}
+{{.:keihin:keihin-jets.jpg?180|}}
+{{.:keihin:keihin-slide-diaphragm-needle.jpg?180|}}
+{{.:keihin:keihin-float-bowl.jpg?180|}}
+  * **Side view**
+    * Air intake from the airbox.
+    * Choke valve seat.
+    * Pilot screw seat.
+    * Duct for the high intake vacuum that acts on the //air cut-off valve// diaphragm.
+    * //Air cut-off valve//: air in (normally open).
+    * //Air cut-off valve//: air out.
+  * **Float chamber**
+    * Main jet
+    * Slow jet
+    * Starter jet (choke/enrichment jet)
+    * Float valve
+    * Breath hole
+  * **Vacuum chamber**
+    * Air intake from the airbox.
+    * Starter (choke enrichment) air supply passage.
+    * Air intake for the //air cut-off valve//: normally open. It closes on deceleration (high rpm + throttle closed).
+    * Air intake for the slow jet.
+    * Air intake for the choke.
+    * Small vent that connects the chambers above and below the diaphragm: it acts as a vacuum/pressure control and damping system.
+  * **Airbox view**
+    * Air intake for the pilot/idle and the //air cut-off valve// circuit.
+  * **Engine view, bottom**
+    * Primary pilot outlet port. This is the main idle fuel outlet, controlled by slow jet and pilot screw.
+    * Pilot progression ports. They provide staged extra fuel during throttle opening.
+  * **Engine view, top**
+    * Starter (enricher) outlet port and vacuum pickup port that operates the //air cut-off valve//.
+  * **Slide, diaphragm, needle**
+    * Slide lift holes: vacuum bleed holes that control how quickly pressure changes reach the above diaphragm chamber.
+  * **Float bowl**
+    * Drain screw.
+    * Drain conduct.
+===== The pilot screw =====
+The Pilot screw is on the engine side of the carb, located after the pilot jet, it is a fuel screw.
+  * Turning it IN (tightening clockwise) reduces fuel flow, leaner mixture
+    * Effects:
+      * Harder cold start.
+      * Lower idle speed.
+      * Possible hesitation off idle.
+      * Lean deceleration popping.
+  * Turning it OUT (loosening counterclockwise) increases fuel flow, richer mixture
+    * Effects:
+      * Smoother idle.
+      * Better throttle pickup.
+      * Easier starting.
+      * Reduced decel popping.
+===== The air cut off valve =====
+{{.:keihin:air-cut-off-valve_transient-enrichment-system.jpg?400|}}
 ===== Web References =====
-  * **[[https://www.motorcycleproject.com/text/how_cv_carbs_work.html|How CV carburetors work]]**
+  * **[[https://www.motorcycleproject.com/text/how_cv_carbs_work.html|How CV carburetors work]]** - {{:tecnica:motori:keihin:www.motorcycleproject.com-how-cv-carbs-work.pdf|Local PDF copy}}.
+  * **[[https://gadgetsfixitpage.com/article.php/the-keihin-cvk-40-carburetor|The Keihin CVK-40 Carburetor]]** - {{ :tecnica:motori:keihin:care-and-feeding-of-the-keihin-carb.pdf|Local PDF copy}}.
+  * **[[https://www.venturerider.org/forum/forums/topic/65604-what-is-the-name-and-purpose-of-this-carburetor-part/|"Coasting enrichment valve" or "air cut-off valve" or "transient enrichment valve"]]**