During periods of increased road loads or high speed operation, the air-fuel ratio must be increased for added power. The added fuel required during this period is supplied by the power fuel system. The power fuel system is controlled by the intake manifold vacuum. Manifold vacuum is transmitted from an opening in the base of the main body, through a passage in the main body and power valve chamber, to the power valve diaphragm. The manifold vacuum, acting on the power valve at idle speed or normal road load conditions, is great enough to hold the power valve diaphragm down, overcoming the tension of the spring on the valve stem, and holding the valve closed. When high power operation places a greater load on the engine, the manifold vacuum drops below a predetermined value, the spring opens the power valve. Fuel from the fuel bowl flows through the power valve and into passages leading to the main fuel system, enriching the mixture. As engine power demans are reduced, manifold vacuum increases. The increased vacuum overcomes the tension of the valve stem spring and closes the power valve.
Warm up your engine. Hook a vacuum meter at the intake point. Engine at idle. Automatic transmission should be in drive. Read the vacuum and cut it in half. That is the valve size.
Example: 13hg. The power valve would be 6.5, 14hg. The power valve would be 6.5. There is no 7 so you round down.
2100 power valves are available for order here
Think you have a bad power valve? Check these things out also:
Venturi cluster air bleeds plugged (Remove the air horn and the cluster, then blow out the passages in the main body and cluster assembly)
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Don’t forget to remove the check ball and weight first!
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Fuel coming out this hole indicates a bad power valve, or improper gasket.
When people say their power valve is leaking or not working, my first thoughts are they installed the power valve incorrectly. The newer power valves use a large gasket that fits into a grove a the edge of the power valve sealing surface. I hold the carburetor upright as I screw the power valve and gasket into the main body. This operation is complete when you see the gasket is securely seated into the grove on the lip of the power valve. If not seated correctly it will damage the gasket and the power valve will leak like it is ruptured!! The same thing will happen if they use the wrong gasket for the two different power valves with different sealing surfaces. The newer power valves use the perimeter thick gasket and the older ones use two different types. One gasket is thick and triangular on the inside ( probably the correct one for Ford 2100 &2150) and round on the outside. The other is thinner in thickness and diameter and has three or four tabs on the inside to keep centered on the power valve. (used more often on spark valve like the 1100 carb) You look at both older gaskets to see if they seal to the mating surface on the main body.
