Bob :
Don't know of a site that discusses those questions, but in general CO
is controlled only by fuel/air mixture. Ignition can play a part, but
only if it is badly off (HC will go way up first). Cam and compression
(also exhaust and intake) play a part only in that they affect fuel/air
(especially with carbs).
However, it's very common for CO to rise with engine speed. Idle
mixture is usually set to stoich for pre-emission cars, and on the lean
side for later cars, both of which give low CO readings. But, as
throttle opening increases (especially into the 'power' zone, however
your carb/PI senses that), the mixture is usually made richer, for
better power and throttle response. Some carbs (like SU and ZS) do this
solely on air flow, some on manifold vacuum, some on throttle opening.
Many use a combination of two or three of these.
For example, the Carter Thermoquad on my motorhome uses a combination of
throttle position and manifold vacuum. At idle, the CO is turned down
to under 2%, but with the original power valve calibration, 2500 rpm
no-load resulted in over 7%. (Due to a mistake at the testing center, I
had to adjust the calibration. Don't recall the final CO, but HC
dropped from 280 to about 170 ppm. Engine ran good before, now runs for
shit.)
The long-ago state test on my then-stock TR3A showed 3.7% at idle, 6.4%
at 'cruise' (which was no-load, 2500rpm as I recall). This was with
'normal' tuning, I had it way lean the first time, with the result it
flunked with a "exhaust leak" <g>
Of course, we're talking before the catalytic converter (if any) here.
I've been told that units similar to the Gunson are also quite sensitive
to exhaust gas temperature. Higher temp = higher CO reading.
Randall
"Westerdale, Bob" wrote:
>
> Hi-
> Does anybody have an authoritative site describing CO emissions
> and the effects of various engine parameters? ( i.e. cam, compression,
> fuel/air,timing,etc.)
> I've been playing with my new Gunson Gastester and am a bit puzzled by the
> increase in CO with engine speed. (No, not in the TR3.)
> Thanks,
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