At 05:53 PM 10/16/96 +0100, you wrote:
>Hi all,
>
>A little late but,
>
>Thanks for all the responses to the fuel mixture question.
>
>A few things I've learned since:
>
>1. The Constant Velocity (what and where CV?) carb works relatively
>simple. Dependent on the throttle disc position and the inlet
>manifold vacuum an air/fuel mixture is sucked into the engine. A
>higher vacuum (I mean higher negative pressure) causes (via transfer
>holes in the carb piston) the piston to rise thereby raising the
>needle and enlarging the jet orifice. In the carburettor housing the
>Bernoulli law is acting: P + .5rho V(^2) = constant. (high air
>velocity/low pressure and vice versa). This needle position versus
>air velocity combination forms the air/fuel ratio.
>Which you want to remain constant over the engine rpm range. However,
>your carburettor isn't aware of this fact (-:
>
>Suppose one blocks the airflow - that is what happens if you use very
>clogged air filters - the vacuum in the carburettor rises and the jet
>is supplying more fuel. You'll get a richer mixture. This is exactly
>what you do when using a choke on a 'normal' fixed jet carburettor.
>
>2. K&N filters do not filter out K (potassium) & N(itrogen)! Nice
>try, Mark;
>
>3. Some remarks, which I've taken at heart: If your SU's are working
>allright, don't f$%k with them.
>
>That's exactly what I did. I thought I'd let you know.
>
Bert,
A few observations here:
Point 1) My understanding is that the position of the piston and thereby
the jet needle is that it is dependant solely on volume through the throat.
Granted volume is a function of pressure differential but with a partially
obstructed filter total volume through the throat is restricted, the lift
on the piston is reduced in proportion and the resulting effective orifice
size is consistant with the air flow. This means the air/fuel ratio remains
consistant but total air/fuel flow to the manifold is restricted. Ergo less
power but still correct mixture.
Point 1a) SU's are "normal". All other schemes are mysterious Rube Goldberg
gadgets with WAY too many moving parts.
Point 2) I can't say for sure but I've never had a problem with potassium
buildup in any car with K&N filters.
Point 3) Truer words were never speaked.
Cheers,
___ \______ Ross MacPherson
/ __ \ __ / /------|) arm@unix.infoserve.net
/ (___)---------/ (___) Vancouver, BC, Canada
1947 MG-TC 3528 1966 MGB-GT
|