Rejetting carb

Discussion in 'Sportster Models' started by stugotts, Sep 2, 2007.

  1. stugotts

    stugotts Member

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    I'm considering installing a Yost Power kit in my factory carb. This past July I purchased a 2005 Sportster. When I cruise at light throttle I can feel it running lean. Feels like wind drag pushing on my windshield, if that makes any sense. Anyway, can anyone give me advice on what might be the best size of jets to use? The bike is a stock 1200c, factory pipes but drilled out, altitude here ranges from 3500ft to 4500ft.
     
  2. glider

    glider Veteran Member

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    I would stay away from the yost if it were my bike, just replace the jets and you will run fine. With the elevation you are at, it would require a bit leaner jetting, something in the 42 low size and possibly the 175 main jet. These are only suggestions because at that elevation it could require different jetting.

    Here's a way of testing the jet size.

    Here's a quick test that will tell you if you have to fat of a jet in the top end....
    Run the bike through the gears into third gear and run third up to 60-70 MPH full throttle, then chop the throttle about 1/8 to 1/4 back and see if the bike either surges ahead or stumbles then recovers.

    If it surges ahead, your jetting is lean
    If it stumbles and recovers , your jetting is rich
    If it makes no difference, you're pretty close.

    Quick and easy, pretty accurate too.



    and read through this for the application of the different jetting

    http://www.hdtalking.com/fuel_and_carb_related_issues/764-twin_cam_cv_carb_rejet_suggestions.html
     
    Last edited: Sep 2, 2007
  3. stugotts

    stugotts Member

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    Thanks for the great advice, i'll pick up some jets and experiment. I'll stay within 1 and maybe 2 sizes of original. Thanks again.
     
  4. glider

    glider Veteran Member

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    Post the outcome as far as size jets if you will.
     
  5. stugotts

    stugotts Member

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    Ok, here's what I found. The original jets were #42 and #180. I replaced the #42 with a #45 and left the #180 as is. I also removed the mixture plug and adjusted it to where the idle speed appeared the highest and most stable. This was about 2.5 turns out. Idle speed ended up at about 850rpm. This might be a tad high but it runs really good there, besides, there's nothing wrong with a little more oil psi. During the road test I noticed a total improvement. No more wavering at 1/4 throttle cruise and the odd exhaust popping during decel is also gone. Real happy! Going to do the girlfriend's sporty tomorrow. Her's is a 2002 rigid mount with #42 and #170. Going to try #45 and #180. Thanks again for the help.
     
  6. glider

    glider Veteran Member

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    Glad it worked out for you and your jetting is about the same after the change as lower elevations so it really didn't make that much of a difference in the higher elevations. With the 2 1/2 turns out it looks as if you are in the right area there with the low jet.

    Thanks fotr the input.