Carburetor Power Circuit Operation
The part-throttle circuit handles normal cruising for maximum fuel economy. However, when the engine is under heavy load, it needs a richer mixture. This enrichment is controlled mechanically by a vacuum-operated power piston and a power valve.
How It Works
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Vacuum Source: The power piston's vacuum channel is routed directly to manifold vacuum (below the throttle plates).
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Normal Cruising: High manifold vacuum overcomes the piston's actuating spring, holding the power piston up and keeping the power valve closed.
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Under Load: When you crack the throttle for hard acceleration or sustain high speeds (typically over 75 MPH), manifold vacuum drops.
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The Trigger: Once manifold vacuum drops below 7" Hg, the actuating spring overcomes the vacuum and forces the power piston down.
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Fuel Delivery: As the piston drops, it physically pushes open the spring-loaded power valve. This allows extra fuel to flow directly from the float bowl, through the power restrictions, and into the main well to enrich the mixture.
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Reset: The valve stays open, dumping extra fuel, until the throttle is lifted and manifold vacuum climbs back above 7" Hg to pull the piston back up.
Service Note: Both the part-throttle and power systems are factory-calibrated. There are no adjustment screws or settings required for either circuit.
