Tuning 28mm Mikuni

Discussion in 'Carburetor' started by dkom95, Feb 22, 2021.

  1. dkom95

    dkom95 New Member

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    Trying to sort out a previously modified setup.

    Previous owner's setup ran well with no dead spots or hesitation:
    -Stock motor and airbox
    -Full FMF exhaust
    -28mm Mikuni w/ 230 main
    -Float height 26mm below gasket seat
    -Needle clip at top position
    -Gunked up fuel inlet-- not sure if that factors in

    My new setup idles and revs fine. When riding, low power in mid and top end. Will not rev high or pull hard. Barely pulls me up a hill. Here are the changes I made:
    -Had to return to stock exhaust header
    -Adjusted float height to 21mm below gasket seat per spec
    -Cleaned gunk out of fuel inlet
    -Using a different fuel line, but it still mates to carb fuel inlet so I'm thinking diameter is fine
    -New fuel filter

    Tried different combinations of needle clip and air/fuel screw starting at 1.5 turns out. It seems to run best on the leanest settings (clip at top of needle, air/fuel screw out around 3 turns). Not a massive difference, but noticeable.

    Tried swapping a smaller main jet from a spare knockoff carb. Not sure on size as it was unmarked. Smaller main jet made some improvement, but still lacking mid and top end power.

    Any guidance would be appreciated.
     
  2. Slydog

    Slydog Active Member Technician

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    Needle and needle jet may not be right. May be to rich? I say that because you are running on the leanest needle position.
    If 3 turns out on air screw achieve highest idle that pilot jet is probably to big.

    Why back to the stock pipe?
     
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  3. dkom95

    dkom95 New Member

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    I swapped the motor, carb, CDI, etc into a fat tire BW200. The Blaster header wouldn't work with the BW frame so I'm using a stock IT200 header.

    I have a new untested theory. I swapped the tank and am now using an ebay special from a Honda Benley 125. While the fuel line fits, it needs to be flexed to get it over the carb inlet. However it slides right over the Benley tank's petcock outlet. I'm thinking I may be fuel starving due to smaller diameter petcock. Planning to test soon.
     
  4. Slydog

    Slydog Active Member Technician

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    Git pics. Those were fun in the 80's
     
  5. BrandonSulik

    BrandonSulik New Member

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    Any update on jetting the 28mm? I bought a new 28mm and having Marjorie issues!
     

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