Carb Tuning
Left: This drawing illustrates what occurs when manifold vacuum is high under low-load situations like idle, cruise, and light acceleration. The step-up piston and rod are pulled down against the resistance of the spring, and the thick part of the rod enters the orifice of the jet. This reduces the area that fuel can flow through and leans the mixture. Right: Under high loads such as heavy part-throttle or wide-open-throttle operation, manifold vacuum drops, and the piston "steps up" to the thinner power step of the metering rod. This is why the thick part of the rod is called the cruise step and the thin part is called the power step. View Related Article
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