Re: [ST] Surging [was: Carbon Fiber Pipes and Helibars]

["Paul O'Brien" <birddogoby@xxxxxxx>]

Rick - Thanks for the tips.  I'll keep these things in mind if I get a CF
pipe.  Interesting what you said about the effects of gasohol and idle
mixture on rpm surging.  The only surging I really can feel on the bike is
when I'm doing low speed/low rpm riding in slow traffic, usually below 2000
rpms.  I have to use the clutch more in these conditions to keep it smooth
than on a carbed bike.  I understand the ST is considered to have excellent
EFI so I'm wondering if my idle mixture needs some adjustment, I'm feeling
the the "gasohol effect" or the condition is considered pretty normal.  I've
only had the bike for 3 1/2 months so I'm still getting the feel for it.
Since you seem to know quite a bit about fueling systems, any ideas about my
low speed surging?

Paul
'02 Blue ST
Seattle


- ----- Original Message -----
From: "Rick & Joyce" <rnjwes@xxxxxxxxx>
To: <ST@xxxxxxxxxxxxxx>
Sent: Sunday, March 02, 2003 3:44 PM
Subject: Re: [ST] Surging [was: Carbon Fiber Pipes and Helibars]


> > > <snip>  the engine is a little snatchy right off closed
> > > throttle, which was not there with the standard tune, but
> > > it's not a big deal.  Has anyone else noticed that?
>
> Paul,
> Low-RPM surging can be caused by improper idle fuel mixture.
> Your '02 has a closed-loop idle trim control which is modifies
> idle CO based on inputs from the oxygen sensor and others.  This
> shouldn't affect running above 1500rpm.  But the O2 sensor only
> 'sees' the mixture from one cylinder, so a bad injector spray
> pattern in another cylinder, for example, wouldn't be detected.
> This was a problem in the automotive arena some years ago and
> manufacturers relocated the sensor(s) downstream to the exhaust
> collector area.  If the 'race pipe' tune were to call for a fuel
> mixture which was dramatically richer than that of the O2
> sensor-controlled idle trim, one might have an abrupt transition
> to open loop around 1500 rpm.
>
> On the pre-'02 ST/RS, loading a new tune is only part of the
> procedure.  The other part is to check and adjust the idle CO,
> which in the US except for CA-spec engines, should be in the
> 2.5 - 3.0% range.  Changing the tune will often affect the idle
> CO, sometimes dramatically.  If a following rider sees black
> smoke during hard acceleration, an over-rich mixture is
> indicated.
>
> Another factor is fuel quality.  My '01 surges horribly on
> 'winter-grade' oxygenated fuel (gasahol), particularly when
> holding a steady throttle in the 4k rpm range.  When I'm out of
> the PDX metro area and can fill up with the normal formula, the
> transformation is nearly instantaneous.  Dirty injectors will
> cause surging as well.  Once in awhile, I add injector cleaner
> with a full tank.
> HTH,
> -Rick in Oregon
> '01 Sprint ST
>
>
>
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