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  • 1 Post By Alfy
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November 29th, 2020, 11:11 AM   #1
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I Ride: Husaberg fs 650 2007
Air cut valve

I am trying to understand how this valve works on the FCR MX 41 of my husaberg 650. I have noticed that a spring presses the pin diaphragm which in turn opens a bypass which adds air into the pilot circuit, making it lean. A duct carries the vacuum signal on the diaphragm which overcomes the thrust of the spring and retracts, closing the bypass which adds air to the pilot circuit. So it makes me think that the engine always works with added air from the passage opened by the diaphragm, and that when you decelerate the excessive vacuum closes this bypass. Does "air cut valve" mean that there is an air bypass always active except when the vacuum "closes it"?

I am saying that the air cut valve does not add fuel in deceleration, but is constantly leaning the pilot circuit, except in deceleration when the vacuum activates the cut.

Last edited by Alfy; November 29th, 2020 at 09:33 PM.
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November 29th, 2020, 11:36 PM   #2
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the Husaberg doesn't have an air-cut valve. at least I didn't think it did!

can you take a photo of it and post it here?

cheers

Taffy
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November 30th, 2020, 12:37 AM   #3
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I m not at home, but this is from spare parts husaberg 650 2007
Attached Thumbnails
Air cut valve-screenshot_20201130-103325.jpg   Air cut valve-screenshot_20201130-103341.jpg  
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November 30th, 2020, 03:05 AM   #4
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Hi Alfy

I will have a look at this sometime but these are my thoughts.

there is no need to do anything when accelerating. the valve I would THINK must be for deceleration. to stop the popping and banging.

they obviously though that it would be worse on the 650s! if there is too much unburnt fuel on the overrun then more oxygen helps burn the fuel in the head rather than the exhaust pipe where it would pop and bang.

Taffy
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November 30th, 2020, 10:20 AM   #5
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This is my carb.
In the center of the photo, in the hole of the brass piece c is a one-way valve which is opened by the diaphragm pin. I repeat it is always open except when a strong vacuum retracts the diaphragm. Taffy would you like an additional hole in the pilot circuit? A second PAJ? I don't think so ... that's why I cut the diaphragm pin to keep the valve always closed (as would be an FCR without air cut valve)
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Air cut valve-img_20201130_190434.jpg  
Thanks from Taffy

Last edited by Alfy; November 30th, 2020 at 10:29 AM.
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