Float Height Importance in Carb Tuning

Discussion in 'Thumpers' started by meat popsicle, Dec 21, 2005.

  1. meat popsicle

    meat popsicle Ignostic

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    http://www.factorypro.com/tech/float_height_adj_procedure.html

    I am surprised by this technical discussion on the influence of float height on carb performance by Factory Pro. Please check out the link above.

    Here is a hook:
    I have never read anyone discuss this here. :dunno
    Anyone? :ear
    More:

    Is this something that should be set or only adjusted when a problem presents itself? With this modifier added to the others, the ocean is getting too deep for me; I feel like I'm drowning...
    #1
  2. Cactus Dave

    Cactus Dave Born to Argue

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    I've never encountered that extensive a discussion - a wee bit overwhelming, particularly if you have ever tried, or had, to make float adjustments. My recommendation: don't mess with it unless you absolutely positively must. Float level adjustments are incredibly sensitive to imperceptible adjustments which make tracking and planning and actually effectuating adjustments difficult. In my experience, it is (fortunately) the rare time that one must adjust a float level. Once you do it, you'll probably join me in not wanting to chase that gremlin again.
    #2
  3. potatoho

    potatoho Cheese and Rice!

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    Float height is a great tool for fine tuning. Sometimes a 0.5mm or 1mm change can remove a slight surge or help you offset a slightly too-rich or too-lean condition without having to use shims.
    #3
  4. meat popsicle

    meat popsicle Ignostic

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    Thank you Catcus Dave for that very reasonable warning. I like the imagery: "Chasing the Gremlin". :nod I consider myself warned.

    But you potatoho, have posted next to nothing. You post has me imagining a fairly one-dimensional problem, yet we all know that is not the case! Aside from the macro-dynamics of intake and exhaust's impacts on one side of the stoichiometric equation,

    and the interplay of the idle jet, needle jet (and jet needle) (and it's adjustment), and main jet (with the air jet modulating the previous paragraph) and settings (low speed idle screw and idle screw) in the usual carb adjustments that variably interplay in adjusting low, midrange, and the top end,

    we now are discussing a further adjustment to the fuel half of the stoichiometry (which I was not aware of): the float height's impact on fuel delivery to the jets... :cry

    I think that this has past the third dimension and entered the fourth; one that is beyond my abilities to comprehend presently. And certainly one that is not facilitated by simplistic posts.

    Perhaps someone would care to discuss why float height has such a non-linear effect upon fuel delivery, especially in a CV carb :evil, and how this facet intertwines (lustfully so the boys at Factory Pro lead me to believe) with the other mignions that supply and relieve my engine. :deal
    #4
  5. ChrisC

    ChrisC Amal sex?

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    Great Holy Jeebus Meat, are you trying to win the "I sound just like Hickson" award? :rofl
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  6. meat popsicle

    meat popsicle Ignostic

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    Fixed. :lol3

    I was hoping that if I could spew forth enough multisyllabic words in obviously contrived and contorted phrases, perhaps dangerously confusing the subject he might feel obligated to sort me out. :D

    Of course I know he is busy at the moment so I will try to be patient and enjoy the peanut gallery (and the few rational skeptics that show up).

    All kidding aside, this float height factor really is news to me and I was hoping for some discussion. I was thinking that perhaps this variable may be the monkey wrench in many a tune up without ever being considered. :dunno
    #6
  7. creeper

    creeper Still alive...

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    I don't want anything to do with this thread... I'm not even here.
    #7
  8. ChrisC

    ChrisC Amal sex?

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    Here's to you and your stoichiometry, Meat....

    Liquid fuel is fed to the nozzle of
    the carburetor venturi, and flows
    due to the vacuum generated by the
    air flowing past the venturi itself,
    and from airflow pulsations generated
    by the piston movement. The
    calibrated jets placed upstream of
    the spray nozzle itself control the
    fuel flow reaching the spray nozzle.
    Motorcycle carburetors are nearly
    always of the needle type and have
    a structural architecture as shown
    in the accompanying illustrations.
    The fuel arriving from the tank is
    held inside a constant level float
    chamber. The liquid pressure head
    on the various jets is relatively constant.
    The difference between the
    float chamber fuel level and the level
    that the fuel must be raised to
    by the inducing vacuum remains
    constant. The float chamber level is
    kept constant by means of a fuel inlet
    valve, actuated by a float that
    follows free surface of the liquid in
    the float chamber. When the float
    chamber level drops, due the fuel
    used by the engine, the float drops
    and opens the valve, so that additional
    fuel can flow from the tank.
    The level of the fuel and float then
    increases, and at a certain point,
    closes the valve until the sequence
    is repeated. The level in the float
    chamber is therefore a calibration
    element of the carburetor, since the
    metered fuel delivery changes with
    float level, and therefore affects the
    mixture ratio. By having a high
    float level, a greater fuel quantity is
    delivered compared to the case with
    a low float level, under all operating
    conditions and for all of the carburetor's
    circuits.
    Adjustment of the
    float chamber level is affected by
    two elements: the weight of the
    float (or of the floats) and the configuration
    of the lever arm that connects
    the float with the valve. By
    installing a heavier float, the free
    surface of the float chamber liquid
    must rise before the float buoyancy
    force balances the increased weight
    making the float rise. The result will
    be a higher float chamber level and
    a richer delivered mixture under the
    same conditions. On the contrary if
    we install a lighter float, a lower liquid
    level will cause sufficient
    buoyant force to actuate the valve
    and therefore the carburetor calibration
    will become leaner. That is
    why floats are classified according
    to their weight (printed on them)
    and calibration standards for their
    position inside the float chamber
    are prescribed in order to assure
    correct operation. To modify the
    float chamber level, if necessary and
    when it's not possible to change the
    Checking the position of the float inside the
    float chamber is prescribed. According to different
    carburetor models, the distance of the float
    from the contact surface of the float chamber
    needs to be measured float weight, in some cases it's possible
    to change the angle of the lever
    that operates the valve.
    In this way, the float closes the valve
    in advance (for a lower level) or
    later (for a higher level) at equal
    weight.
    We must note, however, that too
    low a level in the float chamber can
    result in an insufficient liquid head
    on the jets and therefore lead to the
    risk of dangerous enleanment of the
    delivered mixture.
    This can occur when the fuel moves
    inside the float chamber due to the
    accelerations the vehicle undergoes.
    In these cases (which mainly happen
    on off-road motorcycles or on
    the track, in the bends or under violent
    braking), if the level is too low,
    one of the jets leading to the carburetor's
    circuits may be temporarily
    exposed to air instead of liquid.
    In some versions, special screen baffles
    are applied near the jets.
    These are called bottom traps and
    their purpose is to maintain the
    maximum liquid quantity around
    the jets under all possible conditions.
    A needle that closes on a seat,
    which is inserted or screwed into
    the carburetor's body, forms the
    fuel valve. The needle is equipped
    with a synthetic rubber element on
    the tip.
    This material is perfectly compatible
    with normal commercial gasoline
    but in the case of special fuels
    such as those containing alcohol, it
    is necessary to verify the compatibility
    of the fuel and the seals in order
    not to compromise the carburetor's
    functionality.
    Different versions of the needles are
    equipped with a sprung tip in the
    connection with the float, in order
    to reduce the needle's vibration induced
    by the motion of the liquid
    in the float chamber and from the
    motorcycle's movements.
    The diameter of the needle valve is
    a calibration element since it determines
    the maximum fuel delivery
    rate.
    If the diameter is too small to accommodate
    the fuel quantity that
    the engine requires under certain
    conditions (generally at full load)
    the float chamber empties faster
    than it can be replenished through
    the needle valve! If this condition
    should continue for some time, the
    engine suffers from reduced fuel delivery
    due to the fact that the level
    in the float chamber is decreased
    and therefore the carburation has
    become too lean.
    #8
  9. creeper

    creeper Still alive...

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    You could have tried a little punctuation on that before you pasted and posted... ya' know.



























    Still not here.
    #9
  10. meat popsicle

    meat popsicle Ignostic

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    The Factory Pro boys don't make it sound like that linear of a variable. In fact it sounds downright chaotic... I am starting to think there is some turbulence at work in there; perhaps variable fuel flow rates can significantly differ in their turbulent flow just like the intake air? :scratch Enough to matter? :dunno

    Did I hear something? Sounded like... ah, nevermind. :evil
    #10
  11. creeper

    creeper Still alive...

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    Hey Chris...

    I just remembered where I had read your paste before... it's from the Dell'Orto "Carburetor basic principals" booklet. As soon as I saw the word "enleanment", that was the tip off. :D


    Still not here...

    Hey Meat... wana read some good carb stuff and not the usual basic bullshit? Just scroll down to Dell-Orto General Carburetor Manuals.
    #11
    bikemoto likes this.
  12. cat

    cat Long timer

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    This is what's good about EFI. And you can go buy nice Techlusion /whatever things for them.

    ... The day's coming - and soon - when carbs will seem as stupid, or archaic, as points ignition.
    #12
  13. ChrisC

    ChrisC Amal sex?

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    Fuckin'A Creep, I thought I could get away with looking like one of you smart guys with that post.... and then you outted me. Next time I'll make sure to steal info from more esoteric sources....
    :cry
    #13
  14. meat popsicle

    meat popsicle Ignostic

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    Estoeric Sources?
    Here ya go Chrissy: Dead Men Don't Wear Plaid
    Enjoy! Especially the videos... gawd I love that movie :tb

    PS - Cat, beware of Technology and the revenge of unintended consequences...

    PPS - reading creeper; thanks. :wave
    (EDIT: is that an 'index hint'? you bastage you... :evil)
    #14
  15. potatoho

    potatoho Cheese and Rice!

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    :dunno I just followed the carb manual (gives a range of settings). Hard to quantify it in terms of the course adjustments (jets, clip position). Lemme try to find the web page which I followed..

    Oh haha, it was the same factorypro pages:
    http://www.factorypro.com/tech/carbtune,CV,lower_rpm_engines.html

    I followed that method when I first got my bike, but I didn't want to mess with the float at first, other than setting it to the stock setting. When I started with aftermarket carbs I didn't expect the default float to be correct for my application, and it worked better at a different setting.
    #15
  16. racer

    racer Long timer

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    I have a 05 KLR that fouled a plug while on a trip. The bike ran flawlessly for the first 1500 miles. As I was sitting at stop light after pulling off the interstate, the bike died and was really hard to restart. Wouldn't run unless the trottle was basic wide open. Pulle into the motel parking lot, pulled carb, checked it all out, nothing. Found a fouled plug though. Kaw dealer next day said I did everything they would have done. Its run fine since. I have the T-mod. The only thing I can come up with, is this. about a half hour before the problem, we decended a mountain road which was gravel. My riding buddy was on a big bike and couldn't go fast, so I basically had the trottle closed using engine braking all the way down for maybe ten to fifteen minutes.

    Could this have fouled the plug? Earlier in this post it said CV carbs are usually rich at high and low RPM?

    Any thoughts out there?
    #16
  17. meat popsicle

    meat popsicle Ignostic

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    Did you try the KLR thread (or just make a new one)? They might understand the dynamics of your system or perhaps have some experience with that phenomenon on a KLR. For instance: WTF is a 'T-mod'? :dunno Just friendly advice; not booting ya out - maybe one of the guru's will have some insight and link your problem to this thread's topic. :D
    #17
  18. meat popsicle

    meat popsicle Ignostic

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    Still reading, but just wanted to mention that the forum you linked to has a pdf on EFI that I noticed mentions EFI for 2-strokes... I wonder if that will clean them up enough to get over the hump created by oil injection?

    The article also will lead one to a company that makes EFI systems for small engines, for those of you mainacs working on an EFI conversion for your bike.
    #18
  19. cat

    cat Long timer

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    I know. Like the BMW F650. People seem to love them and no problems with the EFI - or ECM /"black box", actually - but I heard of many guys having problems.

    I just bought an MZ (Yamaha 660 motor with 2 carbs) ... one of the bikes I looked at was the Aprilia Pegaso Strada and one of the things that put me off a bit was the transponder ignition key and the dealer said if you took the instruments off the bike wouldn't run. :huh

    EFI (or ECM, rather) works fine on cars, but somehow I..just don't feel comfortable with my bike having a transponder key (like my Ford, which certainly hasn't given any electronic problems.) I just like as little wiring as possible on bikes.
    But eventually there won't be any bikes with carbs.
    #19
  20. meat popsicle

    meat popsicle Ignostic

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    I got the same feeling from the big BMW GS with it's 'servo-assisted anti-lock brakes (whirrrrr, whirrrrrrr, click, click...); complexity adds that much more opportunity for error or failure unless the system is self-adapting, which is not common in the engineering lexicon (and even then individual bikes can still have problems).

    Agreed on wiring, as it is one of my many weak points... but I continue to worry that EFI will be an Achillies Heel, as I percieved servo-assist anti-lock brakes to be.

    True, EFI is technically far superior to carbs; better fuel efficiency and cleaner emissions (one and the same eh) to name the obvious points. But unless the system can be field adjusted and fixed it will not make a very compelling DS (adventure) system.

    PS - I don't think Ford's been on its game since the 1960s. My F100 was bulletproof; able to leap tall building in a single bound!!! :D
    #20