Whenever I'm pondering the possible cause of something like a hesitation/ stumble concern, I find it particularly useful to draw on the experiences I received tackling drivability issues before fuel injection was the order of things. This especially is true because many, if not most, hesitation problems are fuel-delivery related, and for the most part, an engine is still an engine. In the simple, yet complex world of carburetors, atmosphere is the primary driving force behind fuel deliv- ery. There is a built-in fuel reservoir that has a needle-and-seat at the place where fuel comes from the pump, with that needle sitting on a float arm and its tiny cone-shaped stopper poised to staunch the flow of fuel as the float rises in response to the filling of that reservoir. Furthermore, that float has to be adjusted to stop the flow of fuel into the reservoir whenever the fuel level is at the right depth. If the reservoir level is too low, the demand might not be met; if the level is too high, unwanted fuel might begin to siphon and dribble into the intake through the venturi.
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