Carburator Assembly

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JamesK
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Carburator Assembly

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Hi all,

Hope you can help me, like a total noobe I forgot where one of the hoses is supposed to reconnect to.

I pulled out the carbs to check them over, to try to fix a rough/poor idle problem. Now that I am trying to hook the carbs back on the bike I can't seem to figure out where one of the hoses is supposed to connect to. As you can see from the pic below this is the hose that connects to the lower part of the carb. The upper one is already connected to the airbox.

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vaty
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Re: Carburator Assembly

Beitrag von vaty »

Hi JamesK

it seems to be a hose from the VTV system

Kind regards

Vaty
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Re: Carburator Assembly

Beitrag von vaty »

That me again :P

I found another picture. I have collored the VTV-System hose red.

Good luck

Vaty
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AoS
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Re: Carburator Assembly

Beitrag von AoS »

That hose in the picture (the big one between the two carb bodies) is open and is just held by a box-shaped clip on the top right of the airbox. It is not related to the VTV at all.

Right now I don't know much about its function, but it is called a ventilation hose ("Entlüftungsschlauch") in the German manual. It doesn't seem to draw much air or otherwise it would be connected to a filter element. It's probably there to admit atmospheric pressure to the carbs.

Hope that helps,
Dirk
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Re: Carburator Assembly

Beitrag von JamesK »

Thanks for the suggestions guys, but I don't think they are correct.

@Vaty, I already have the VTV all hooked up, and the only other hoses in the area are accounted for. The one running down towards the back wheel connects to the fuel tank (water release I think it's called in the manual). The second thinner ID hose connects to the fuel tank on the On/Pri/Res valve. The third one, on the diaphragm chambers can only fit between the top of the carb and the airbox.

@Dirk, are you sure about this? That hose, if left unplugged would be sucking in unfiltered air strait into the head and cylinders. I was thinking that if I can't figure out where it's supposed to plug in I'd block it off or at least stick a small air filter on it. The other idea if it does like you say need to suck in some air is to connect it to the blocked off hole on the airbox. I don't have a picture of this handy but at least it would be getting filtered air.

I have highlighted in orange the hose I'm talking about?

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Re: Carburator Assembly

Beitrag von JamesK »

On a related topic, has anyone here removed the silly PAIR system? I have done it on my other bike which has EFI so it was easier to figure out which hoses and parts where not needed :roll:

I would really appreciate any advice from people who have successfully removed the useless PAIR system on the XF650 as I'd like to do that while I'm in there.
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vaty
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Re: Carburator Assembly

Beitrag von vaty »

Hi JamesK :)

Dirk is on the right way :streichel:
I have found another drawing.
The hose located on and between the top of the carbs is called "air control hose". It´s the yellow one in the drawing.
The hose you are looking for is called "air vent hose", painted red.

Best regards
Vaty
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Re: Carburator Assembly

Beitrag von JamesK »

Guys, thanks a lot for the clarification. I'm never comfortable having unfiltered air coming into the engine or carbs so I was wondering does anyone see a problem with plugging this hose into the currently unused hole in the airbox as shown in blue in the updated diagram?

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Re: Carburator Assembly

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For my unstanding unfiltered air does not enter the carbs through the air vent hose.

The carbs are working like the venturi principle. So the carbs need an ambient air pressure to adjust the correct air and fuel flow.
When you plug the air vent hose, the carbs are adjusted with a static ambient air pressure. I don´t know what happens during, for example, different weather conditions with different ambient air pressure. It could be possible, that the carbs are not working correctly. Same happens during a drive from sea-level into the mountains. The actual ambient air pressure will change in this situation and the carbs are not working correctly.

So never plug this hose

Take care

Vaty
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Re: Carburator Assembly

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vaty hat geschrieben:For my unstanding unfiltered air does not enter the carbs through the air vent hose.

The carbs are working like the venturi principle. So the carbs need an ambient air pressure to adjust the correct air and fuel flow.
When you plug the air vent hose, the carbs are adjusted with a static ambient air pressure. I don´t know what happens during, for example, different weather conditions with different ambient air pressure. It could be possible, that the carbs are not working correctly. Same happens during a drive from sea-level into the mountains. The actual ambient air pressure will change in this situation and the carbs are not working correctly.

So never plug this hose

Take care

Vaty
Thanks again Vaty and Dirk. I just finished reassembling the carbs back on the bike per your suggestions. She started up pretty quickly and ran fine while cold. Unfortunately as before (even though I didn't quite realize previously) once the bike warmed up it started stalling (would not idle) again and becoming hard to start.

I suspect now that it must be something to do with either part #25 - Sensor Assy or #12 - Valve Assy, Solenoid. If I had to guess, I'd say Sensor Assy, since this unit controls the butterfly valve position and I would guess is connected to temperature sensor of some kind.
I am still trying to figure out whether the #12 - Valve Assy, Solenoid is part of the PAIR system, does anyone know?

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Re: Carburator Assembly

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There are two different systems we have to speak about:

On the one hand there is the vacuum system that regulates how fast the piston valves rise, especially in gears 2 and 3, for the purpose of noise reduction. The solenoid, the sensor and many of the vacuum tubes are related to that system. The sensor also seems to time the ignition. Some say that you can safely remove all of this, but I'd keep the sensor and just get rid of the solenoid and the tubes. You can connect the tube number 5 (please check, I'm not entirely sure) in your diagram to the vaccuum side of the fuel tap and remove all the thin tubes, the solenoid, the vaccuum chamber and the check valve.

On the other hand there is the PAIR system meant to reduce emissions. But I don't know much about it since we don't have the PAIR on the German versions of the XF.

(The original shop manual has some very concise explanations on the carbs and the different systems. I could send it to you if your inbox can stand a ~13 megabyte file.)

Dirk
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Re: Carburator Assembly

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AoS hat geschrieben:There are two different systems we have to speak about:

On the one hand there is the vacuum system that regulates how fast the piston valves rise, especially in gears 2 and 3, for the purpose of noise reduction. The solenoid, the sensor and many of the vacuum tubes are related to that system. The sensor also seems to time the ignition. Some say that you can safely remove all of this, but I'd keep the sensor and just get rid of the solenoid and the tubes. You can connect the tube number 5 (please check, I'm not entirely sure) in your diagram to the vaccuum side of the fuel tap and remove all the thin tubes, the solenoid, the vaccuum chamber and the check valve.

On the other hand there is the PAIR system meant to reduce emissions. But I don't know much about it since we don't have the PAIR on the German versions of the XF.

(The original shop manual has some very concise explanations on the carbs and the different systems. I could send it to you if your inbox can stand a ~13 megabyte file.)

Dirk
Dirk, thanks for the explanation, btw, I already have a copy of the shop manual. For example it mentions that to check the solenoid valve you should hear it click, which I could not. For the butterfly valve sensor assy I will be checking today as that should move/turn since that's it's function.
I was simply hoping to get some ideas/experience from all you guys figuring that you might have previously seen/fixed this kind of problem.
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Re: Carburator Assembly

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I'd just throw out all the unnecessary parts to reduce possible origins for the error. But I can't imagine that the vacuum system affects idling in the way you describe.
There is no temperature sensor, and the sensor on the butterfly valves just registers the position. Together with a gear sensor the information is used to limit the speed and level of the piston valve by bypassing ambient pressure to the diaphragm. If the solenoid has broken it shouldn't change much, this just disables the system. As far as I know sensor also times the ignition but the engine seems to run just as well without it.

Have you cleaned all the jets? Is the fuel level set correctly? Does the choke work? Is everything sealed airtight? Have you adjusted the idle screw? And I would check the valve clearance.

Dirk
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Re: Carburator Assembly

Beitrag von JamesK »

AoS hat geschrieben:I'd just throw out all the unnecessary parts to reduce possible origins for the error. But I can't imagine that the vacuum system affects idling in the way you describe.
There is no temperature sensor, and the sensor on the butterfly valves just registers the position. Together with a gear sensor the information is used to limit the speed and level of the piston valve by bypassing ambient pressure to the diaphragm. If the solenoid has broken it shouldn't change much, this just disables the system. As far as I know sensor also times the ignition but the engine seems to run just as well without it.

Have you cleaned all the jets? Is the fuel level set correctly? Does the choke work? Is everything sealed airtight? Have you adjusted the idle screw? And I would check the valve clearance.

Dirk
Thanks for the advice Dirk.
I pulled the carbs off again, removed all the jets, basically all 3 brass things between the floats. Blew air through all of them, ran a thin wire through all the holes, nothing looked to be clogged up. Also pulled out the Air mixture screws and made sure those holes were not blocked, turned the air mixture screws all the way in, then 2.5 turns out. Also checked the float plungers, they looked fine too.

Put everything back together and still have the same problem, the bike won't idle once the engine warms up.
I've not checked the valves, but they should not be due for adjustment yet.
Not sure what to check next...
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Re: Carburator Assembly

Beitrag von JamesK »

Well, the problem is fixed, but it's nothing I've ever heard of before, or would have guessed.
I'll PayPal $10 to the person who guesses the correct answer :wink:
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