Re: IML: 1967 Imperial Coupe / Carburator Help

[dardal@xxxxxxxxxxxxxxx]

Quoting Mike Pittinaro <mechimike@xxxxxxxxx>:

> > The adjustments in mixture mentioned above in this
> > message referred to idle
> > mixture only, and will have no effect on normal load
> > mixture strength.  The
> > only way you can change the operating mixture is by
> > replacing jets.
> 
> Actually, on the Edelbrock and Carter carbs, with the
> 2 front metering screws, the screws yes do affect idle
> mixture, however they do somewhat affect the mixture
> at off idle.  Their "contribution" if you will,
> decreases at higher and higher throttle, though.  
> 
> I'm not sure how this works, but this is what I have
> been told about these carbs.
> 

Here is how it works, as far as I know.  The idle circuit feeds gas with a small
outlet just below the closed throttle plates.  The driving force for this flow
is engine vacuum, as you have vacuum just below the throttles (the venturies do
not produce any vacuum at idle because the flow is too low).  As the throttles
open, the throttle plates move down and go past that fuel port.  So now, the
fuel port sees atmospheric pressure, and the flow stops.  I can see how there
may be a "transitional" range where both the venturi and the idle circuit may
feed the engine., and so the idle adjustments may have some effect.  However,
this will be at very low loads, and will certainly have no impact on whether
the engine knocks or not, because that happens at higher loads.  In my
experience, my 440s only knock at WOT.  But both of my 440s have larger than
stock cams and the carbon on the pistons and heads has been turned into green
house gas long ago.

D^2


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