PAIR valve testing on '01 SV650S

Discussion in 'Motorbike Technical Discussion' started by User Bp, Dec 31, 2013.

  1. User Bp

    User Bp Guest

    What is the range of manifold vaccum for which Suzuki's PAIR system
    an an '01 sv650s acually does something? The existing system seems
    to allow air injection at manifold vaccum below about 450 mm, or
    about roughly 18" Hg. It seems to close off completely at vacuum
    greater than about 20".

    The spec in the manual is fairly close to unintelligible, though
    it's tempting to think that PAIR operation is allowed at extreme
    high and low manifold vacuum, with a cutoff in the mid-range. It
    makes sense after a fashion, since HC emission is an issue mostly
    at low speed (low combustion temps) and WOT (rich mixture).

    The wording in the manual (including typos) is:
    "Apply nefative [sic] pressure slowly to the control valve and blow
    the above manner." Meaning to blow in the direction of intended airflow,
    I think. So far, so good. Now the fun part:

    "If air does not become flow out within the specification the control
    valve is normal condition". Next, it says:
    "Negarive [sic] pressure range 230-400 mm HG"

    Does anybody know the intended meaning? I take it to mean the PAIR system
    should admit fresh air to the exhaust when the manifold vacuum is below
    230 mm or above 400 mm. If so, that's not what happens and might explain
    some rough running problems.

    Thanks for reading,

    bob prohaska
    User Bp, Dec 31, 2013
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  2. User Bp

    Mark Olson Guest

    The only thing I know for sure, is that the air injection system
    should allow air into the exhaust ports under some amount of manifold
    vacuum. But to be honest I would simply cap off the vaccum fitting
    at the carb(s), and also cap the PAIR air intakes and forget about
    it. The only way I can see the PAIR valve affecting how the engine
    runs, is if there is a vacuum leak. You might get some popping in
    the exhaust but it should not affect how the engine runs.

    The only engine problem I ever had with my SV in 40k miles whas when
    I managed to incorrectly reassemble one of the carb tops, and the
    diaphraghm got pinched, causing the slide on that cylinder not to
    lift. Other than that, it always ran like the proveribal top. I did
    install one size larger pilot jets and also shimmed the needles with
    washers supplied by a helpful guy on the SV forum.

    (former 2001 SV650S owner)
    Mark Olson, Dec 31, 2013
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  3. User Bp

    User Bp Guest

    That seems to be the general habit. I was hoping for a hint as to
    the designer's intent.
    There's a slight off-idle stumble and an intermittent miss at
    small (25mph) throttle openings. The bike was much smoother
    at acquisition (2k miles) and only showed the ill behavior at
    around 12k miles. Putting a hand over the airbox inlet raises
    the idle speed initially, but it's not clear how to interpret
    this given that CV carbs are to some extent pressure-compensating.
    Likewise, this bike ran perfectly on acquisition. Thus my hesitation
    at sledgehammer fixes.

    Thanks for replying!

    bob prohaska
    User Bp, Jan 1, 2014
  4. User Bp

    Mark Olson Guest

    I wouldn't characterize removing the PAIR system as a "sledgehammer
    fix". Many owners remove them simply to make access easier, and it
    won't make the bike run any better or worse. IOW, if you're looking
    at the PAIR system in an attempt to fix a stumble/miss, I would look
    Mark Olson, Jan 1, 2014
  5. User Bp

    User Bp Guest

    Ok, sorry, figure of speech. It remains surprising that nobody seems
    to know how the PAIR valve is supposed to work.
    It'll certainly improve access. It would be very helpful if the idle
    screws could be adjusted while running.
    That's a valuable clue. I pulled and cleaned the carbs once to no effect,
    in fact they weren't even very dirty. Thus my suspicion that the PAIR
    valves might be part of the trouble. Seems like maybe I need to look again.

    Thanks for writing,

    bob prohaska
    User Bp, Jan 2, 2014
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