Carby too lean or to rich?

Discussion in '2-Stroke Engines' started by linnix13, Sep 13, 2009.

  1. linnix13

    linnix13 Banned

    so i have a 33cc zooma, anyways, it has one ajustment screw on the carb, i asume in is lean and out is rich, with it turned 1 1/2 out it bogs in the lows but is great in the highs, if i turn it out 2 times it runs great in the lows but then gets really rumbly in the highs, i tried in between but it seems to be either rumbly or boggy, and there is never exhaust smoke, not on 2 turns or one and a half,
     

  2. GearNut

    GearNut Active Member

    It depends on where the screw is located on the carb.
    Typically, if the screw is located near the air cleaner then it controlls air flow.
    If the screw is closer to the engine then it controlls fuel.
    This is in no way a steadfast rule though.
    I would set the screw to run best at low speeds and then see what adjustments are possible for just the hi speed fuel circuit. Perhaps you need a different fuel jet? If your carb has a jet needle, you may need to adjust the clip setting.
     
  3. linnix13

    linnix13 Banned

    its a dead simple carb, it has no pin ajustments, one screw, on the bottom of the carb, next the the 2 fuel lines,(they both go to the gas tank but one sucks and one blows)
     
  4. GearNut

    GearNut Active Member

    Can you post a picture of it?
     
  5. linnix13

    linnix13 Banned

  6. GearNut

    GearNut Active Member

    OK. That is near identical to the carb that came on my Go Ped.
    Look at the center of the black plastic throttle cam, where the inner cable attaches to the carb. There should be a tiny little screw.
    That controls the low speed circuit mixture. The screw on the side of the carb is like an adjustable main jet. It controls the high speed mixture.
     
  7. linnix13

    linnix13 Banned


    oh ok, so how abouts do i adjust it? the problem was that it would bog at full throttle and only drive on 3/4ths full, and it wouldent climb hills, turning the high speed mixture fixed the bogging but it hampers the highs,
     
  8. linnix13

    linnix13 Banned

    so do i turn the low speed counter clockwise or clockwise?

    and how mutch?
     
  9. GearNut

    GearNut Active Member

    There should be 3 screws total.
    1 idle speed
    2 idle mixture
    3 high speed mixture
     
  10. GearNut

    GearNut Active Member

    I am holding that exact carburetor in my hand right now.
    The screw by the fuel hose barbs is the high speed screw. Turn it out to add fuel, in to reduce fuel.
    Looking down at the black plastic cable cam there is a brass screw with slots on either side of it. Do NOTtry to turn the big brass screw. It is hollow in the center with a super glue filler in it.
    Pick put the glue as best you can, or, I burrned it out with a small "pencil" torch. It lights up really fast and "poof" it is all gone. It burned so fast the large brass screw never had a chance to get hot enough to melt the plastic any.
    Be carefull to only apply the flame to the center of the brass. Do not get it near the plactic.
    After you remove the glue plug you will need a jeweler's screwdriver to turn the tiny screw down in there.
    Out to add fuel to the idle circuit.
    In to reduce the fuel.
    There really is no midrange adjustments on these carburetors.
     
    Last edited: Sep 13, 2009
  11. linnix13

    linnix13 Banned


    ok but it idles great and is fine in the lows, its the transition between low and high that it boggs, and i can fix the bogging by running it on 3/4ths choke, so i asumed it was runing lean, so i turned the high speed screw out about half a turn and voila runs great in the lows(very very powerfull more than it has ever been!) and it transitions just fine, but in the highs it sounds like a lawn trimmer(which the engine is) and then just stays at that speed, which is like 25-30kph and for a 33cc engine pulling a 230lb me seems fair, im not sure the engine is designed to scream, it will scream if it was lean but wont all 2 strokes do that before they blow up? its this engine here,
    http://azmotoparts.com/uploads/2008_6_2575446.jpg
     
  12. GearNut

    GearNut Active Member

    You definately need to turn the idle speed screw out to add more fuel to the idle circuit. That is the tiny screw under the glue cap. You will also have to adjust the idle speed screw, the long screw opposite where the cable attaches to the carb.
    In 1/8 turn increments, turn the idle screw in or out untill the idle speed is good.
    Next, turn the mixture screw in untill the idle starts to stumble. Try to clean up the idle speed with the speed screw. Keep doing this untill the turning the speed screw only results in the engine dying. Next, turn the tiny mixture screw out about 1/8 to 1/4 turn and leave it there.
    Now set the idle speed screw again to get a good idle speed and leavt it there.
    You must get the idle speed circuit happy first.
    Then can you adjust the high speed screw near the fuel hose barbs.
    You need to adjust the high speed circuit under operating loads, not just sitting on a block with the wheel spinning up in the air.
    Adjust, ride and test, adjust, ride and test, ect.
    Adjust it in untill the engine starts to sputter and cut out (too lean).
    Next turn it out in 1/8 turn increments untill the engine starts to blubber and loose power (too rich). Count the number of screw turns starting from when it was too lean to when it got too rich.
    Your goal is to set the high speed screw in the middle.
    Divide the counted number number by 1/2 and use that resulting number to count the turns the screw needs to be turned back in.
    All should be well untill vibration causes the screws to loose adjustment some time in the future (inevitable).
     
    Last edited: Sep 13, 2009
  13. Hajuu

    Hajuu Member

    haha hmm, my carb only has one screw and I was almost sure it was the idle speed :/

    Id assume most kit carbs would be the same if they only have 1 screw, but im probably wrong
     
  14. Hajuu

    Hajuu Member

    Oops didnt see there was another page :D
     
  15. GearNut

    GearNut Active Member

    I never did find out if I helped him get it to work right. He never posted his results. All I can say is that what I posted is what I was taught by a go-ped guru. I did it exactly as I described and my go-ped screamed like a banshee and started easily, hot or cold.
    Before I tinkered with it, it was a bear to get started and it was gutless at speeds.
     
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