I'm confused on how to differentiate mixture control from the main metering system, and why we even need one at all. Let's say we had a large resovior, and a needle type mixture control system. The differential pressure would push/pull fuel from the discharge nozzle at our set mixture ratio? Then where does the need for the main metering system come in?
Float-type carburetor
Any help is appreciated, thank you!
IF I understand your question, you're asking why we need a main metering system with any moving parts. It sounds like your assumption is that, as the throttle is opened, the increased airflow should pull a commensurately larger volume of fuel through the jet to keep the mixture correct. In a rough sense, that's true, but... That passage is a limiting factor, and as fuel demand increases, it becomes less efficient and the mixture suffers. Because there is such a wide throttle (airflow) range, it is more efficient to have a graduated, or stepped increase on the fuel inlet side. Find a diagram of an old motorcycle carb for a simple image of this. Most of them use a tapered needle in a main jet which is opened wider via the accelerator cable.
as shown, the main metering system is the portion of the carb which is active through most of its operating range (i.e., when not idling, for which you have an idling system, and when not accelerating, for which you have the accelerator pump system). So the point of your question is not clear, because without the main metering system, you wouldn't have a functioning carb of this type.
