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Thread: Airbox holes

  1. #1
    Junior Member Mywasp's Avatar
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    Airbox holes

    Should they be taped over?
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  2. #2
    Senior Member admiral's Avatar
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    Yes, most likely they should be taped over or otherwise plugged
    Last edited by admiral; 02-25-2016 at 10:40 AM.
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  3. #3
    Senior Member small's's Avatar
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    You can get solid rubber plugs at ace hardware or whatever your local hardware store is..
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    Senior Member admiral's Avatar
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    Ignore
    Last edited by admiral; 02-25-2016 at 10:39 AM.
    Hidden Content A ride in the woods helps me relax and release tension. The fact I'm dragging a body should be entirely irrelevant?

  6. #5
    Senior Member Fred's Avatar
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    The stock air box's snorkel intake is not really restrictive. However if one makes the assumption that is and drills holes to somehow try to let more c.f.m. in ( it really won't), why would one think this extra cubic feet per minute of air will somehow make the bike run leaner?
    If one assumes one gets higher air flow rates through the carburetor it will just stimulate more fuel to be sucked through various fuel circuits resulting in same stoichiometric ratios, just at a higher c.f.m. One has to remember the Bernoulli principle and how it makes our carburetors work. Increasing the air flow rate for any given throttle opening will be accompanied by a corresponding increase in the fuel flow rate; it will not alter the air/fuel ratio which is determined by all the fuel passageway orifice sizes, not air flow rates.
    I know there is lots of shade tree wisdom and old wives tales repeated out there, also lots of gimmicks for sale. Doesn't mean they work.
    If one wants to lean out the air/fuel mix one needs to change the fuel metering to reduce fuel delivery rates. Simply trying to cram more air through simply grabs more fuel with that additional air; the ratio is mechanically fixed by the physical geometry of the various fuel orifices all driven by suction caused by the air flow according to the Bernoulli principle. Besides the drilled holes let more induction noise out while allowing a tiny bit more debris and air in.
    Last edited by Fred; 02-25-2016 at 07:36 PM.
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  7. #6
    Senior Member admiral's Avatar
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    Quote Originally Posted by Fred View Post
    The stock air box's snorkel intake is not really restrictive. However if one makes the assumption that is and drills holes to somehow try to let more c.f.m. in ( it really won't), why would one think this extra cubic feet per minute of air will somehow make the bike run leaner?
    If one assumes one gets higher air flow rates through the carburetor it will just stimulate more fuel to be sucked through various fuel circuits resulting in same stochiometric ratios, just at a higher c.f.m. One has to remember the Bernoulli principle and how it makes our carburetors work. Increasing the air flow rate for any given throttle opening will be accompanied by a corresponding increase in the fuel flow rate; it will not alter the air/fuel ratio which is determined by all the fuel passageway orifice sizes, not air flow rates.
    I know there is lots of shade tree wisdom and old wives tales repeated out there, also lots of gimmicks for sale. Doesn't mean they work.
    If one wants to lean out the air/fuel mix one needs to change the fuel metering to reduce fuel delivery rates. Simply trying to cram more air through simply grabs more fuel with that additional air; the ratio is mechanically fixed by the physical geometry of the various fuel orifices all driven by suction caused by the air flow according to the Bernoulli principle. Besides the drilled holes let more induction noise out while allowing a tiny bit more debris and air volume in.
    Anyone's seat-of-the-pants opinion seems more wishful thinking than anything that can be substantiated by imperial evidence and the physics of fluid mechanics.
    Fred,

    Despite your thinking that drill holes in the airbox cover won't work, I'm telling you it does. As it was about 10 years ago when I tried it, I can't for the life of me remember who it was here on the forum that suggested this idea with the airbox holes.

    But I did indicate the best way was to re-jet and the airbox holes should be considered only temporary.

    If you get a spare airbox cover, try drill holes in it and see if you can tell the difference. I'll even loan you my modified airbox for you to test. Now, I'm not gonna say you will fall off the back of your TW when you crack the throttle, but you will be able to hear the difference even at idle with a slightly higher rpm.
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  8. #7
    Senior Member Ski Pro 3's Avatar
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    I can not see the TW200 able to utilize a less restrictive air flow than what is stock. The motor just isn't capable of pumping any more air through than is already available. I recommend plugging the holes and maintaining the air filter regularly.
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  9. #8
    Senior Member admiral's Avatar
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    OK, I am wrong and you all are right.
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  10. #9
    Senior Member small's's Avatar
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    take your air filter lid and filter out and and try to ride youe bike down the road wide open. It will prolly start spitting and spuddering over about half throttle. It will make a difference..
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  11. #10
    Super Moderator Purple's Avatar
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    I find myself in the curious position of both agreeing with Fred, and agreeing with Admiral — though Fred did temporarily make my brain hurt with “stimulate more fuel to be sucked through various fuel circuits resulting in same stochiometric ratios, just at a higher c.f.m” — although he did redeem himself with “the ratio is mechanically fixed by the physical geometry of the various fuel orifices all driven by suction caused by the air flow according to the Bernoulli principle” — that at least I could (barely) understand.

    Fred — yes — your theory works in “principle”

    And yet I can “see” how Admiral’s theory would work in practice — otherwise why would we need to re-jet when putting K&N type filters on there ?

    If you have a finite maximum fuel flow (determined by the main jet size), then increase the air-flow (the holes) - or more realistically “reduce the resistance to air flow” — then that fuel flow still remains finite.

    It may not apply until the main jet is “full on” — but you can see where my thinking is coming from ……

    (That’ll teach the pair of you to give me a headache) …….
    TWilight likes this.
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