PAIR valve testing on '01 SV650S

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

 

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)

 

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

 

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
elsewhere.

 

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