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  1. #1
    alindo01's Avatar
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    sluggish in 1/4 - 1/2 throttle only

    OK guys i need your help. I restored an '04 Polaris 700cc single Keihin carb. Idle to 1/4 throttle is fine and 1/2 to WOT is also fine but it is sluggish almost bogged down on 1/4 - 1/2. All fuel lines are brand new and the carb was rebuilt with all original parts. The problem existed before I replaced the fuel lines and the rebuilt the carb and it is still there after (although a little better). What else can I check?


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Is this a 2004 Virage or 2004 Freedom?

    What jet sizes are installed in the Keihin carb?

  3. #3
    alindo01's Avatar
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    What's up K447, it's an '04 Freedom but now that you mention that I belive the carb came out of an '04 Virage. I though I checked on the manual and the jets were the same for both.

  4. #4
    alindo01's Avatar
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    Hi K447,

    This is what I have but I have not verified the jets, I only cleaned and rebuilt. Can I open the carb while it's on the intake manifold?

    Freedom / Virage Carburetor Specifications
    Carburetor Manufacture Keihin
    Size 40mm / 38mm Venturi
    Fuel Regulator System Diaphragm
    Float Arm Level 1.5mm
    Starter System Choke
    Main System Primary Main Jet: 148
    Secondary Main Jet: 120
    Mid Range System #42
    Pilot System #58


  5. #5
    alindo01's Avatar
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    Still boggs

    OK guys, I just finished checking the jets in the carb and they are correct. Pilot #58, mid range #52,Main 148, secondary 120.

    So what else can I check that would cause it to bogg down 1/4 - 1/2 throttle?

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Have you checked the basics?

    Cylinder compression, intake reeds, water in the electrical box, correct spark plugs...

  7. #7
    alindo01's Avatar
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    Compression: yes both are good. +\- 145 lbs
    Reeds: inspected them before they went in
    water in the box: nice and dry
    correct spark plug: NGK BPR8ES .024 in.

    I just don't get why it only afects the mid range.
    Someone mentioned to spray carb cleaner while the engine is running around the intake manifold and to check if the idle goes up which would indicate a vaccum leak but I wanted to check with you guys first.

  8. #8
    johnsonmtz's Avatar
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    Quote Originally Posted by alindo01 View Post
    OK guys, I just finished checking the jets in the carb and they are correct. Pilot #58, mid range #52,Main 148, secondary 120.

    So what else can I check that would cause it to bogg down 1/4 - 1/2 throttle?
    I'm not up on Keihn carbs, but it sounds like the fuel circuit for that range has a problem.

    First you need to determine the exact nature of the bog. Does the engine blubber, spit and sputter and then eventually 'clears out' and it takes off after 1/2 throttle? If this is the case, that means the fuel circuit responsible for that throttle range is over fueling and causing a rich condition.

    Or, does the engine fall completely flat on it's face in that throttle range? If you pull the choke lever does the engine pick up and go? If this is the case, the fuel circuit is not providing enough fuel and it's running lean in that region.

    Are there needles that you can adjust on these carbs or do you only have the fixed jets? IF you have needles, try turning low speed according to your bog type and try again. If you're rich, turn it in to reduce fuel, if you're lean turn it out to increase. If you are stuck with fixed jets, I would guess the problem is that mid-range jet. Again, you'll need to adjust jet size according to the bog (smaller for rich, larger for lean). Of course there is also the possibility the fuel circuit that supplies this range has a problem.

    Sorry for no answers, but it's a few things to think about.

    KJ

  9. #9
    alindo01's Avatar
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    KJ,
    I will give it a world this weekend and play around with the choke and try to determine if it leans out or too rich.

    The single carb has only one needle for the Low, all others are fixed jets.

    Question: By fuel circuit you mean the internal path in which the fuel take for that range of throttle right? So since that is a fixed path, how can it be adjusted besides changing the jet?

    Sorry I'm relatively new to this....

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