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Thread: Another Carb Question

  1. #1
    4 Cycle Advanced User
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    Another Carb Question

    Down by the bowl drain plug is an adjustment screw with a tapered needle. Is that the bowl air vent circuit or is that a fast way to drain the bowl? Should I close it off, is it some kind of adjustment, what does it do?


    Thanks,
    Sundog

  2. #2
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    It is a drain. If you take it completely out, be careful putting it back in because the "O'' ring on it is easily damaged. Close it off when cranking the engine or fuel will spill from the carb bowl drain fitting on the bottom. Also be careful trying to screw it in too hard or it will be extremely hard to drain the fuel later. I've seen people who could not even drain their fuel with the screw from tightening the screw too tight. It's almost easier to drain the bowl by removing the brass carb bowl drain plug on the bottom. Also, if you do drain from the brass plug, be sure the "O" ring on the plug does not stick to the bottom of the bowl and get knocked off and lost. Don't ask me how I know both of these "O" ring problems.

  3. #3
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    Ok, so it should be closed while running. Thanks

  4. #4
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    When that needle is screwed in all the way does it still pass air. If not how does the bowl get vented? Why does that line need a catch can, should the needle be open a little?

  5. #5
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    The carb bowl is vented through a small brass nipple that sticks out of the side of the carb. Look or feel underneath it you will find the opening. The over flow tube goes to a catch can so fuel does not flow out onto the pavement they do dribble a little on hard corners.

  6. #6
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    If the level of fuel in the bowl is too high, it will flow out of the bottom drain. The drain serves two purposes. If the fuel level is too high in the bowl while running, the extra flows out of a brass tube in the bowl that flows out the drain in the bottom of the carb. The same drain in the bottom of the carb will let all the fuel out the of the bowl when you back the drain screw out slightly. As stated above, there is also a brass nipple on the side of the carb that is a air feed/bleed that is intended to keep pressure above the fuel level in the bowl at atmospheric pressure.

  7. #7
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    Thanks guys, I get it now and the drain tube is in a separate catch can.

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