The added fuel for high power operation is delivered by the power enrichment system. A vacuum passage in the throttle body transmits manifold vacuum to a chamber which contains the power valve. The power valve, sometimes called the economizer valve, has a neoprene diaphragm exposed to the vacuum in the chamber.
At idle and cruising speeds, the vacuum acting on the diaphragm holds the valve closed against the compressed load of the spring at the top of the valve. When high power demands reduce manifold vacuum beyond a predetermined point, the spring expands, opening the valve.
Fuel from the float chamber flows through the center of the valve and out of calibrated holes in its side which meter the fuel. The fuel flows through passages to both main wells where it joins the fuel flow of the main metering system, enriching the mixture for full power operation. Restrictions in the passages provide equal distribution of fuel to both main wells.