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YICS Chamber Missing Passages XJ650J

Discussion in 'XJ Technical Chat' started by Tombez, Jan 12, 2020.

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  1. Tombez

    Tombez New Member

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    I opened up what I believe to be the YICS chamber on my XJ650J '82 Maxim to clean it, only to find there are no visible passages connecting to the chamber. My engine and frame shorty VINs match, both starting with 5N8 which I believe indicates XJ650J, and my title indeed says a 650cc '82 Maxim.

    My first thought was that maybe the middle layer of the engine has been replaced, taken from a model without the YICS system, but why would Yamaha go through the effort of drilling the chamber out?

    I have some pictures, but it won't let me post with them in the thread, I'll try to comment them.

    1. Am I just not seeing the passages?
    2. Is this part of my engine from another model XJ?

    Thank you for taking the time to read and maybe respond. :)
     
  2. Tombez

    Tombez New Member

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    Attached pictures of my engine with the YICS chamber bolt off, YICS chamber with and without flashlight.
     

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  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    there is a video in this thread where if you look closley at the 10:00 position on the wall you will see the small holes
    YIKES!: ALL ABOUT THE "YICS" SYSTEM.

    2ed half of video looks like there are more holes on the 2:eek:o position

    gun solvent and a cleaning rod will help clean the passage . them there is small tools you can clear the passages with

    this is ports bottom of head
    holeshead.PNG

     
    Last edited: Jan 12, 2020
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  4. Tombez

    Tombez New Member

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    I had read that post, but hadn't watched the video, thank you. Those passages are tiny! Now I'm not surprised I can't see them.
     
  5. Door dude

    Door dude Active Member Premium Member

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    Question... Does the yics tube chamber fill up with the air fuel mix from all 4 carbs and each cylinder draws from the chamber or does each cylinder draw from its own carb ? Im thinking from the chamber.
     
  6. XJ550H

    XJ550H Well-Known Member Premium Member

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    the vents make the fuel swirl as it goes into combustion chamber for more efficent burning

    the chamber sucks in air and fuel that is remaining in between the carb and valves when the valves close and then into the carb/ valve area feeding the cylinder on the intake stroke

    from link YIKES!: ALL ABOUT THE "YICS" SYSTEM.

    Here is how Yamaha describes their YICS system:

    "The YICS consists of 2 separate chambers, each connected, to a port on each cylinder just behind the intake valve. As the piston moves down on the intake stroke, the cylinder fills with a fresh air/fuel charge. A vacuum is also created in the YICS chamber at the same time. When the intake valve closes, part of the charge is drawn into the YICS. When the intake valve reopens the mixture in the YICS shoots back out through an angled tube into the cylinder, mixing with and swirling the main intake charge. The swirling charge is then compressed and ignited, burning more completely and producing more power than that of a conventional engine."

    read the post for even more info
     
    Last edited: Jan 14, 2020

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