The power enrichment system remains basically unchanged. This system furnishes the enriched mixture needed for efficient performance during high power operation. Manifold vacuum, which is strongest at the idle, decreases as the load on the engine is increased. The power enrichment system is operated by this decreased manifold vacuum. If there is a strong manifold vacuum, it acts on the economizer diaphragm to keep the power valve closed. When manifold vacuum is reduced below a certain point, the power valve is opened, enriching the mixture.