Carb sync clarification 2
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Thread: Carb sync clarification 2

  1. #1
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    Question Carb sync clarification 2

    hi. yesterday i pulled my carbs out for a bench sync before doing the actual manometer sync. this is what i observed while syncing them.

    balance screw "c" changes only the #4 carb.
    balance screw "a" changes only the #1 carb.
    balance screw "b" changes only the #2 carb.

    but i have read and seen many posts which mentioned that the balance screw in the middle ( "b" ) changes both #1 & #2. so that's why it's used to balance the carb as pairs ( #1+#2 to #3+#4 ). so i double checked it again but i could see that it changed only the #2 carb. has anyone tried it and noticed this ? if balance screw "b" changes the #2 carb only, how can we use that screw to balance carbs as pairs ( #1+#2 to #3+#4 ). please share your experience and give some advice. thank you.


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    Last edited by Bikeboom; 19th March 2017 at 01:20 AM.

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    Think of it like three see-saws (or teeter totters, depending on where you're from). Screw A when turned one way will open carb 1 while closing carb 2 at the same time, and if turned the other way will close carb 1 and open carb 2. Screw C does the same for carbs 3 and 4. Then, once you've got the two pairs of carbs balanced off their mate, you use screw B to balance the pairs together, so if you turn the screw one way it'll open both carbs 1 and 2 together whilst simultaneously closing carbs 3 and 4, or if you turn the screw the other way it'll close carbs 1 and 2 at the same time as opening carbs 3 and 4. Does that make sense?
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    Quote Originally Posted by phreak911 View Post
    Think of it like three see-saws (or teeter totters, depending on where you're from). Screw A when turned one way will open carb 1 while closing carb 2 at the same time, and if turned the other way will close carb 1 and open carb 2. Screw C does the same for carbs 3 and 4. Then, once you've got the two pairs of carbs balanced off their mate, you use screw B to balance the pairs together, so if you turn the screw one way it'll open both carbs 1 and 2 together whilst simultaneously closing carbs 3 and 4, or if you turn the screw the other way it'll close carbs 1 and 2 at the same time as opening carbs 3 and 4. Does that make sense?
    thank you very much. but mate i'm pretty sure they are not working as see-saws. are you 100% sure ? coz i've used paper stripes just to check the butterfly openings while paying attention for both carbs at once when i'm adjusting the screws. i'm pretty sure they work independent. and for an example the #3 and #4 carbs can't work like see-saw. coz #3 is our master and it's only adjusted by the idle screw which affect other 3 carbs too. am i right ? thank you again.

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    Biker phreak911's Avatar
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    Check your bike manual, but I'm 100% sure what I described is accurate. It's the same on pretty much every four cylinder carburettor setup bike. I've been doing this for a few years now...
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    Quote Originally Posted by phreak911 View Post
    Check your bike manual, but I'm 100% sure what I described is accurate. It's the same on pretty much every four cylinder carburettor setup bike. I've been doing this for a few years now...
    i'm talking about the CBR250RR model. are you talking about the same bike ? thank you very much. i'll check it again soon
    Last edited by Bikeboom; 20th March 2017 at 08:27 PM.

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