[ Bert: Sorry I don't have any answers, only questions. ]
Bert Otten writes:
>
> Recently I purchased the much appraised MGB K&N filter set to swap
> for the standard pancake filters on the double HS4 setup. (the
> 'standard' setup for a B!)
> I bought them from MOSS and the vendor told me that probably, since
> the air flow would be less restricted, I'd to install new, richer,
> needles as well, otherwise the engine could be running too lean.
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?
--
Todd "A little knowledge is a dangerous thing" Mullins
Todd.Mullins@nrlssc.navy.mil On the lovely Mississippi (USA) Coast
'74 MGB Tourer with twin HIF4s
"I could go at any time..."
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