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Pinned How to: bench sync your carbs

Discussion in 'Tech Tips' started by Th3_Huntsman, Mar 12, 2014.

  1. Th3_Huntsman

    Th3_Huntsman Senior Member Contributing Member

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    Hi guys

    As many of you may know I have recently rebuilt my first set of carbs using the excellent litetek seal kit.
    One thing I did not realise was as I had my carbs completely apart after putting them back together I had changed the sync of the butterflies. I'm a rookie I know!

    So for those of you who do change your carby seals in the future following is a Howto sync the carbs whilst they are not on your bike. Please be aware this method isn't perfect but does put them back to the factory setting. It also gives your mechanic a benchmark and will make it easier for them to perfectly balance your bikes carbies.

    Firstly lay your carbs down as below
    image.jpg
    The aim is to adjust the butterflies to open in unison, personally the method I used was my eye and the 5 little centre holes below
    image.jpg
    So with the butterflies closed turn your idle screw to set the benchmark carb ( far right) I did it so the butterfly splits the top hole in half and I can't see the lower hole
    image.jpg
    Next step is to turn the screw that controls the adjacent carb
    image.jpg
    Use these 3 screws which control the butterfly to the left of each

    Beware to snap open the throttle linkage after you think you have set each butterfly perfectly to check it is still the same!

    Good luck and happy spannering!
     
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    Last edited: Mar 12, 2014
  2. Th3_Huntsman

    Th3_Huntsman Senior Member Contributing Member

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    Before syncing.



    After a bench sync



    see the difference around 6-8krpm?
     
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  3. Revolver

    Revolver Big Member Premium Member

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    Handy piece of info here! Look at the vids later.
     
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  4. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Sounds a thousand times smoother :thumb_ups:
     
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  5. Th3_Huntsman

    Th3_Huntsman Senior Member Contributing Member

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    that was cold as well after setting the idle warm it now snaps down to idle properly :)
     
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  6. cal

    cal Well-Known Member Premium Member

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    nice dude, makes a huge difference
     
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  7. Th3_Huntsman

    Th3_Huntsman Senior Member Contributing Member

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    After 12 months of owning an 80s inline 4 you learn some things lol
     
  8. cal

    cal Well-Known Member Premium Member

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    should get ur own set of vac gauges to polish her off :) or see if chris has a set
     
  9. Th3_Huntsman

    Th3_Huntsman Senior Member Contributing Member

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    I'm actually getting a set as I will have 3 bikes to do soon enough. So yeah already on it mate!
     
  10. cal

    cal Well-Known Member Premium Member

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    whats the seal kit worth? my zxr carbs are due also :idk:
     
  11. Th3_Huntsman

    Th3_Huntsman Senior Member Contributing Member

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  12. cal

    cal Well-Known Member Premium Member

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    can't argue with that price, no doubt i will find some "artefacts" lurking inside my old carbs :lolsign:
     
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  13. RosscoM

    RosscoM Active Member Premium Member

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    my bike is tuned to E;) I synchronised my carburetors to E, that is, using an E string off a steel string guitar, its used as a 0.1 mm feeler gauge between the butterfly plate and the carburetor bore where the 5 holes are in the picture above, and far more accurate than the human eye... Also, you should set them all from no 3 carburetor, as that's the one the idle is set off and the throttle cable pulls on, and 0.1 mm will still be way above the factory 1600 rpm setting, so once they are all open at 0.1 mm wind the idle screw right back till it isn't touching the throttle linkage, then wind it in till it just touches, then another 1/2 a turn in.

    set no 3 carburetor with your ad-lib feeler gauge by the idle screw till you can feel the butterfly plate lightly dragging when the gauge is moved up and down the carburetor bore, then set carburetor 2 to the same drag, then set carburetors 1 and 4 the same. A fraction of a turn on the adjusting screws either way and it will be too tight to move the gauge or too loose, it's a delicate touch required.

    before synchronising with a manometer or vacuum gauges, valve clearances and spark plug gaps (or new spark plugs) must be set, I would also rough set the mixture screws at the factory 2 turns out, as all these items will affect the fuel burn and vacuum drawn through the carburetor. I would also suggest adjusting the eXup valve if your bike runs one prior to synchronising
     

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