You can think of it as the jets controlling just how rich full rich is, and the red knob as a way to eliminate the excess fuel as desired.
This is correct in a sense but it misses the main point. A carb is a volumetric device, mixing air and fuel according to a volume ratio. As we climb, though, a fixed volume of air contains less oxygen. Thus, to maintain the right chemical ratio of fuel to oxygen the amount of fuel must be reduced = Leaning.the mixture control fine tunes the air fuel ratio?
It's actually both. To provide detonation margins and keep CHTs low enough that the aluminum heads don't lose much strength during high power operation, a much richer mixture is needed vs when in cruise flight (a leaner mixture also works but produces less power). So during climb you can lean gradually to maintain the same air/fuel ratio you had at lower altitude and once you level off and reduce power you can lean much further for efficiency (also here operating lean of peak EGT is more practical than during climb with a NA engine).Yeah... I believe the real goal is to maintain air/fuel ratio as air density varies with altitude, not to lean it out.
When the MA#SPA is on the idle circuit fuel is sucked out of the float bowl by the low pressure at the edge of the throttle valve, that is the only time the idle circuit will be in effect. As the throttle valve is opened the low pressure at the edge of the throttle valve goes away and is replaced by the vacuum created by the venturi.How does carb jetting relate to the mixture control?
Is it that the jetting needs to be close, then the mixture control fine tunes the air fuel ratio?
Thanks Skip