Differences

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--- tecnica:motori:honda_ntv650_carburetor [2024/09/23 12:15] – [The air cut off valve] niccolo
+++ tecnica:motori:honda_ntv650_carburetor [2025/12/19 13:08] (current) – [Repair kits] niccolo
@@ Line 1: / Line 1: @@
 ====== Honda NTV650 Revere - Carburetor ======
-The Honda NTV650 Revere mounts two **Keihin** vacuum piston carburetors. Each carburetor has also an **air cut-off valve** driven by a small membrane.
+The Honda NTV650 Revere mounts two **Keihin** vacuum piston carburetors. When servicing the carburetors, it must be kept in mind that in addition to the **vacuum piston diaphragm**, there is also a small diaphragm that operates the **air cut-off valve**.
 Here it is my experience in **replacing the diaphragms** and some information on the little-known **air cut-off valve**.
@@ Line 25: / Line 25: @@
 As soon as they were mounted, the result seemed good: the precision and sensitivity of the throttle was significantly improved compared to the old cracked membranes. In a few months I will check the actual seal of the membrane and especially of the glue. The one supplied reports among its characteristics a maximum operating temperature of 80 °C. Probably the Loctite 454 has better characteristics.
-In the following picture you can see the mounting position of the diaphragm, seen from below:
+In the following picture you can see the mounting position of the diaphragm. You can see the angle with the vertical axis measuerd on the top cover and a view of the piston from below:
-{{.:honda_ntv650:diaphragm-position.jpg?200|Diaphragm original position}}
+{{.:honda_ntv650:carburetor-diaphragm-alignment.png?240|Diaphragm alignment}}
+{{.:honda_ntv650:diaphragm-position.jpg?240|Diaphragm original position}}
 ===== Jets and pilot screw =====
@@ Line 43: / Line 44: @@
 The **factory settings** are likely to be for a **very lean mixture** at idle, which is also why the cut-off valve is needed. This setup is required to meet stringent pollution regulations. It may be that the best idle performance is achieved with a richer mixture (pilot screw turned out more than two turns). A richer idle also reduces the possibility of afterburn (exhaust popping) when the throttle is released.
-===== Hoses position =====
+===== Fuel and breather pipes placement =====
-In the following photos you can see how the fuel line and the breather tube are positioned around the carburetors. This is how I found them in my 1991 Revere, but I found other models having the breather tube going to the right side, in a mirror-like way.
+In the following photos you can see how the fuel line and the breather tube are positioned around the carburetors (the lower end of the breather pipe should be inserted into the binder, together with the fuel pipe). This is how I found them in my 1991 Revere, but I found other models having the breather tube going to the right side, in a mirror-like way.
 {{.:honda_ntv650:ntv650-revere-carburetor-front-bottom.jpg?200|}}
@@ Line 51: / Line 52: @@
 {{.:honda_ntv650:ntv650-revere-carburetor-rear-bottom.jpg?200|}}
 {{.:honda_ntv650:ntv650-revere-carburetor-rear-top.jpg?200|}}
+===== Carburetors synchronization =====
+Remove tha tank and connect two vacuum gauges to the cylinders intakes using two joints plugs (Honda part 16214-MB0-000). Provide the fuel in some way, warm up the engine and adjust the idle speed (1100 +/- 100 rpm). The difference in vacuum reading should be 40 mm Hg or less.
+If necessary, synchronize to the specification by turning the synchronization adjusting screw: screwing-in by **turning clockwise will increase the idle of the rear cylinder**.
+{{.:honda_ntv650:sync-carb-ntv650-a.png?direct&280|Carburetors synchronization: Plug}}
+{{.:honda_ntv650:sync-carb-ntv650-b.png?direct&280|Carburetors synchronization: Joint plug}}
+{{.:honda_ntv650:sync-carb-ntv650-c.png?direct&280|Carburetors synchronization: Adjusting screw}}
 ===== The air cut off valve =====
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 Il circuito della valvola cut-off è un **condotto complementare al circuito del minimo** e contribuisce con una sua parte alla miscela aria-benzina per il corretto funzionamento del minimo. La differenza è che in tale circuito il condotto dell'aria può essere chiuso creando temporaneamente un maggiore apporto di benzina. La valvola cut-off viene azionata da una membrana collegata al condotto di aspirazione: quando la depressione è molto alta (alti regimi di rotazione e valvola a farfalla chiusa) la membrana fa chiudere il condotto dell'aria cut-off; il risultato è una miscela più ricca che evita l'afterburn. Quando il motore scende di giri la depressione diventa minore e la valvola cut-off torna nella posizione di riposo; il circuito del minimo viene quindi riportato alla condizione normale.
+===== Repair kits =====
+You can find several carburator **repair kits** on the net, many of them are no-branded, mainly Chinese production. What you want to replace mostly will be the **float chamber gasket** and the **valve needle**, whose rubber may have hardened and deformed. It is nice if the kit contains also the other o-rings.
+{{ .:honda_ntv650:kh-1348-box-back.jpg?120|Keyster KH-1348 kit}}
+{{ .:honda_ntv650:kh-1348-box-front.jpg?120|Keyster KH-1348 kit}}
+I found that several kits have low quality and/or low design parts, especially the float chamber gasket may be too thin or does not perfectly fit the cave. A nice exception is the kit from **Keyster**, a Japanese company specializing in carburetor restoration kits. I purchased the **KH-1348 kit** specifically produced for the Honda NTV650 Revere 1988-1990 and it turned out to be of **excellent quality**. The kit contains:
+  * 2 x Gasket chamber
+  * 2 x Valve seat with washer, filter and needle
+  * 2 x Screw air with spring, O-ring and washer
+  * 2 x Drain screw with O-ring
+  * 1 x Jet main #140
+  * 1 x Jet main #135
+  * 2 x Jet slow #42
+{{.:honda_ntv650:kh-1348-content.jpg?200|KH-1348 Kit Contents}}
+The kit **does not contain** the stem holding the main jet nor the little oval gasket of the air cut-off valve, but I was **particularly pleased with the float chamber gasket**: the shape and size are perfectly similar to the original.
+It seems that also the Keyster kit **K-976EK** is compatibile with the NTV650 Revere, it contains fewer parts, but it contains the same rubber parts as the **KH-1348** kit, plus the oval O-ring of the air cut-off valve. Another kit from Keyster is the **K139** (also labeled **NTMOR-007G**), which includes only the float chamber gasket.
 ===== Web References =====