Strange carb modification - help needed
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Thread: Strange carb modification - help needed

  1. #1
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    Question Strange carb modification - help needed

    hi. recently one of my friends bought a CBR. he complained that when he pickup from the 2nd gear there was some kind of loss of power. so we removed the carburetor to inspect first and then clean.

    surprisingly we could see some metal sheets wrapped around the float just above where the float plunger touches the float . mixture screw settings were 3/4 out in all 4 carbs!. we already know that these float heights are not adjustable and mixture screw settings are totally wrong. anyway jet sizes were ok and they were in stock sizes. we removed those metal pieces and put it to the standard screw settings and balanced. now the bike runs fine.

    But can someone explain what that previous owner / mechanic had done to this carb ? what is the purpose of those metal pieces wrapped around the float ? what it could have done to the float level and fuel supply overall ? and why is that pilot screw settings are totally out. we checked the plugs. one plug is ok and other 3 had kind of black carbon soot on them.

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    thank you.
    Last edited by Bikeboom; 8th April 2017 at 06:57 PM.

  2. #2
    Biker phreak911's Avatar
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    From what I can tell (on my tiny phone screen), someone has tried to create a thicker stopper underneath the float valve, which would push it closed earlier, thus lowering the fuel level in the float bowel. I can't remember the exact effect of lowering the float level, I think it leans the mixture out in the rev midrange? Someone else might be able to shed more light on the matter. Not sure why you'd want to do this. If the bike has an aftermarket "free-flow" exhaust and / or intake, that would already cause the motor to run lean, you'd want to be adding fuel to get the motor running nicely again... (IMO...)
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  3. #3
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    Quote Originally Posted by phreak911 View Post
    From what I can tell (on my tiny phone screen), someone has tried to create a thicker stopper underneath the float valve, which would push it closed earlier, thus lowering the fuel level in the float bowel. I can't remember the exact effect of lowering the float level, I think it leans the mixture out in the rev midrange? Someone else might be able to shed more light on the matter. Not sure why you'd want to do this. If the bike has an aftermarket "free-flow" exhaust and / or intake, that would already cause the motor to run lean, you'd want to be adding fuel to get the motor running nicely again... (IMO...)
    thank you very much. i thought the same. but if someone can explain the effect of too much float height and low float height it would be great

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  5. #4
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    Quote Originally Posted by Bikeboom View Post
    thank you very much. i thought the same. but if someone can explain the effect of too much float height and low float height it would be great
    You probably live somewhere that has emissions testing. Lowering the float height will lean out the mixture at midrange and lower CO emissions at the expense of power.
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    Biker Slipry's Avatar
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    Bike, it took me a while to find a page I once looked at once upon a time

    hope it is of some help

    Float Height Importance in Carb Tuning | Adventure Rider
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    Quote Originally Posted by ekaftan View Post
    You probably live somewhere that has emissions testing. Lowering the float height will lean out the mixture at midrange and lower CO emissions at the expense of power.
    yea we thought the same. thank you very much.

    Quote Originally Posted by Slipry View Post
    Bike, it took me a while to find a page I once looked at once upon a timehope it is of some helpFloat Height Importance in Carb Tuning | Adventure Rider
    thank you very much. this is very helpful.
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