Differences

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--- tecnica:motori:honda_ntv650_carburetor [2024/09/13 11:19] – [Jets and pilot screw] niccolo
+++ tecnica:motori:honda_ntv650_carburetor [2024/09/24 12:31] (current) – [Replacing the diaphragms at 100.000 and 200.000 km] 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**.
 ===== Replacing the diaphragms =====
@@ Line 14: / Line 15: @@
 Unfortunately, mother Honda **no longer produces the spare part** (code 16112MN8014)! There are at least **three types of non-original membranes** adaptable to the NTV650, which differ in the way they are installed. One type requires cutting the upper plastic ring (the black one) which is then put back in place and glued. A second type requires that the black ring be removed and thrown away (it is the **[[http://www.motorradbay.de/dateien/librane.pdf|Librane]]** model seen in the following photos), the replacement membrane is held in place with cyanoacrylate glue. The glue supplied is gel type, resistant to petrol and high temperatures. Finally, there is a model that must be installed like the original, inserting it in the space between the red and black rings.
-The following photos show the installation of a //Librane// type membrane.
+The following photos show the installation of a //Librane// type membrane, but **I definitely prefer the type that fits exactly like the original**; inserting the replacement diaphragm into the slot using a credit card is quite simple and does not require permanently modifying the piston.
 Before removing the old membrane **mark the point** on the piston that corresponds to the membrane slot, because the new one will have to be positioned **at exactly the same angle**. The black ring can be cut with a cutter and removed. The groove can be cleaned and degreased with synthetic thinner. Be careful to spread a very thin layer of glue, so that the membrane enters well into the housing without encountering any thickness.
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 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:
+{{.:honda_ntv650:carburetor-diaphragm-alignment.png?240|Diaphragm alignment}}
+{{.:honda_ntv650:diaphragm-position.jpg?240|Diaphragm original position}}
 ===== Jets and pilot screw =====
+{{ .:honda_ntv650:main-jet-135.jpg?110|}}
+{{ .:honda_ntv650:main-jet-140.jpg?110|}}
 The **main jets are different sizes** in the front and rear cylinder carburetors.
@@ Line 33: / Line 41: @@
 The **pilot screw** is used to regulate the air-fuel ratio for the engine idle speed; turinig it counterclockwise enrich the mixture (more gasoline). The default setting is **2 turns counterclockwise** from the full-seated position.
+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.
+===== 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 (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|}}
+{{.:honda_ntv650:ntv650-revere-carburetor-front-top.jpg?200|}}
+{{.:honda_ntv650:ntv650-revere-carburetor-rear-bottom.jpg?200|}}
+{{.:honda_ntv650:ntv650-revere-carburetor-rear-top.jpg?200|}}
 ===== The air cut off valve =====