Todd,
Maybe it is like this: If the carb inlet is restricted, such as by
an inefficient air filter, the vacuum in the inlet region (between
throttle plate and filter) would increase. This vacuum would pull in more
fuel past the needle -> richer mixture.
OTOH, maybe this effect is in fact negligable, I don't know.
Ulix
On Thu, 10 Oct 1996, Todd Mullins wrote:
> Can somebody explain this to me? I thought the whole purpose of the
> Constant Velocity carb design was to maintain the mixture at a certain
> velocity (to improve low-rpm power), irrespective of the volume of air
> being sucked in. At a given altitude, the percentage of oxygen in the
> air is (assumed) constant, right? So as RPMs rise, the engine demands
> more air, which raises the piston and needle, which enlarges the jet
> orifice, which permits proportionately more gasoline to flow,
> maintaining stoichiometry.
>
> Now a set of K&N filters will allow more air per unit time to flow, but
> they cannot increase the oxygen content of that air (can they?). If the
> amount of oxygen is the same as for stock filters, then why do we need a
> richer needle? In fact, why manufacture more than one needle per carb
> size, since the needle's only purpose is to maintain a stoichiometric
> ratio of air & fuel, which ONLY depends upon the sizes of the respective
> orifices? At high altitudes, you may raise the jet a bit to compensate,
> but the needle profile shouldn't change, should it? Isn't stoichiometry
> sacred?
Ulix __/__,__
.......................................................... (_o____o_).....
'67 Sprite
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