883 jetting questions

Discussion in 'Engine, Fuel and Exhaust' started by pitbull883, Oct 12, 2016.

  1. pitbull883

    pitbull883 Member

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    Hi. A little over a month ago i replaced my SS super E carb with a stock cv carb. All in all it runs much better with this carb. However, sometimes i will get a cough at the carb, when riding slow, like if i hold the throttle, slightly open. After that it seems fine. I am not sure how many turns the idle screw is out right now, but I am sure it's at the point where i should not turn it much more, i just got off of it and dont want to burn my hand more. I was told that it had the stock jets from an 883 (the guy i bought the carb from did a 1250 conversion and installed an ss carb). I wish i wrote down exactly what jets were in it when i had it apart. Also, the bike has straight pipes. Anyways, does it sound like a jetting problem? Could the straight pipes be causing it to run lean?
    Thanks.
     
  2. Jeff Klarich

    Jeff Klarich Well-Known Member Contributor

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    Mods such as different exhaust and adding more air will lean it out. You may want to rejet, my guess that should help your issue.
     
  3. pitbull883

    pitbull883 Member

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    Thanks. Looks like i should take it apart soon and see what's in it for jets, and take it from there.
    Thank you
     
  4. Jeff Klarich

    Jeff Klarich Well-Known Member Contributor

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    If it's still stock jetting I think you'll benefit from going a bit bigger.
     
  5. kdaddy

    kdaddy Active Member

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    As everyone said. If its a cough on initial acceleration or from takeoff, bump your slow jet one size. Start with 3 turns out and you should be in the ballpark. If the carb still has the plug covering the slow jet, drill it with the smallest drill you can find just till it breaks through. Lightly screw in a sheetmetal screw and pull it out. Screw out the jet and scree in the new one. Very very lightly seat it all the way in. Back it out 3 full turns.
     
  6. Jack Klarich

    Jack Klarich Expert Member

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    3 turns is too too much, change your jet and washer up the slide
     
  7. pitbull883

    pitbull883 Member

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    Im not sure how many turns out the mixture screw is now, my plan is: count how many turns out, find out what jets are in it now, write that information down so i remember, my memory is terrible these days, then get the next jet up. I'm hoping to have time soon, life has been crazy lately.
     
  8. Jeff Klarich

    Jeff Klarich Well-Known Member Contributor

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    Good deal, let us know your results.
     
  9. pitbull883

    pitbull883 Member

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    I sure will. I appreciate the help. Thank you.
     
  10. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    There are a few things to consider when re jetting and setting up a carb
    Get the float set correctly to ensure there is sufficient fuel to feed the jets
    Understand the basic principal of how a carb works ie air flowing through the throat of the carb is drawn by the downward motion of the engine piston
    The shape of the carb throat causes the air passing through to accelerate the fast flowing air will create a depression /vacuum on any still air areas
    The vacuum will draw fuel from the float bowl through the jets the fuel hitting the fast flow of air will vaporise into a fuel/air mixture
    The slow jet feeds the idle port and the transfer port main jet feeds only its own port
    when the engine is at idle the throttle butterfly is almost closed and the main feed of fuel will be from the slow jet through the idle port this can be adjusted by means of the idle mixture screw
    As there will be some air drawn through the throat of the carb some fuel will also be drawn from the main and transfer ports
    The main jet is restricted by the slide needle which is tapered as the slide move up the slide needle opens up more of the main jet
    when the throttle butterfly is opened a wee bit more air is drawn through the carb a wee hole in the slide allows a vacuum to draw the slide up allowing air to flow through the carb emphasis on fuel here is the slow jet and transfer port although the idle port and main port also allow fuel to be drawn
    further opening of the throttle butterfly will increase the air flow and vacuum and draw the slide further up and further on to the taper of the slide needle opening more of the main jet port

    If the slow jet is increased in size then the idle mixture screw can be used to restrict the flow of fuel to the idle port to get a good idle speed and the slow jet will also allow more fuel to the transfer port this will help overcome a lean area at lower throttle openings
    However if the idle mixture is good a few washers under the slide needle would raise the needle further on to the taper and increase fuel at all throttle openings when enlarging the main jet by .5 think of each washer as .1 to give a finer increment in jet size
    Only make 1 change at a time try the bike see how it is understanding what adjustment will influence what throttle opening is important as making the wrong adjustment can make the bike a pain to ride

    Brian
     
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