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Thread: What are these hoses attached to the airbox?

  1. #1
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    What are these hoses attached to the airbox?

    I have my tank off to fix bad solder joints in the electrical feedthrough, and I got to wondering whether I should replace some old hoses while I've got things apart. There are several hoses coming off the airbox and going to a fitting near the cam cover or the intake manifolds, and I'm not sure what they are. The manual just says they're "hoses." I assume they have a slight vacuum. Maybe the ones to the cam covers are to allow excess puked oil to go somewhere reasonably safe?

    Can anybody tell me what I'm looking at in these pictures (I marked the cam-cover-to-airbox hoses with yellow, and the intake-manifold-to-airbox hoses with purple.). I think the intake tubes just go to capped off stubs; perhaps they originally went to the emissions charcoal cannister or something?
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  2. #2
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    I would say- start here-

    https://en.m.wikipedia.org/wiki/Cran...ilation_system

    That explains what you have marked in yellow.

    The capped tubes, as far as I know, are drains. (Capped so that you can see if there is excessive drainage= potential problems.)




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  3. #3
    apriliaforum expert RAS's Avatar
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    top to bottom.
    The clear hose (purple) is an oil drain from the air box. It'll have a plug at the lower entension in that pict. I believe the fat black hose labelled yellow is one of the hoses that goes to the stepper. There should be another just like it going to the other TB. These rubber hoses get very hard over time and should be replaced.

    Middle pict - purple hose is used to sync throttle bodies there's another just like it going to the rear TB. They'll also be plugged with a rubber bit.

    The yellow marked hose in the middle and bottom picts is the crankcase breather hose and why the air box on these bikes gets nice and oily inside. That hose will also get stiff with age and eventually leak oil onto the outer spark plug of the rear cylinder

  4. #4
    apriliaforum prov-nov
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    Ah, the bit about using them to sync the throttle bodies explains everything! There's all these hoses, and they're all capped! It's the sort of maintenance-convenience thing I'd install myself on a Japanese bike, when the factory just caps the sync nipples directly.

    And the crankcase breather makes sense too, per @ansleywynn's Wikipedia link.

  5. #5
    apriliaforum expert RAS's Avatar
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    Quote Originally Posted by spacewrench View Post
    Ah, the bit about using them to sync the throttle bodies explains everything! There's all these hoses, and they're all capped! It's the sort of maintenance-convenience thing I'd install myself on a Japanese bike, when the factory just caps the sync nipples directly.

    And the crankcase breather makes sense too, per @ansleywynn's Wikipedia link.
    That dang crankcase breather allows oil vapor up into the box and eventually does this to a fairly clear filter. There wasn't even a whole to of oil in there. It was just a misted wet everywhere.
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