enrichener
The choke of a motor vehicle.
enrichener: the choke that fattens the fuel mix
The enrichener is a mechanical valve fitted to the intake manifold or carburetor of a spark-ignition engine, designed to increase the proportion of fuel relative to air in the mixture supplied to the cylinders during cold starting and warm-up. It works by restricting the volume of intake air, which lowers the pressure in the manifold and draws more fuel from the carburetor's float bowl into the engine. The term describes both automatic enrichening devices and manual chokes operated by a dashboard lever.
Cold air entering a cold engine reduces the rate of fuel evaporation from the carburetor spray. An enrichened mixture, running at air-fuel ratios closer to 8:1 or 10:1 instead of the normal cruising ratio of 14:1 to 15:1, provides enough liquid fuel to ignite reliably despite poor vaporization. Without enrichment, a cold engine will crank repeatedly without firing or will fire erratically. Once the engine warms and the manifold and intake valves heat up, evaporation improves and the enrichener must gradually lean out the mixture or the engine runs rich, wasting fuel and fouling spark plugs.
Automatic enricheners use a bimetallic strip or wax-filled capsule that responds to coolant temperature. As the engine warms, the sensor element expands and progressively closes the enrichement air bleed or opens a bypass path, returning the mixture toward normal proportions. Manual enricheners, common on older vehicles and small engines, require the operator to push in a knob or lever when starting and gradually withdraw it as the engine warms. The term choke, though still widely used in the trade, refers to the air restriction itself rather than its enrichening function.
Enricheners were essential components of carbureted engines from the 1920s onward. Modern fuel-injected engines perform cold-start enrichment electronically by commanding the injectors to open longer during cranking and warm-up, eliminating the mechanical device entirely. On vintage and current small-engine equipment, particularly chainsaws, outboards, and lawn machinery, manual or automatic mechanical enricheners remain standard. Malfunction, such as sticking closed or remaining partially open, is a frequent cause of starting trouble and rough running in carbureted engines.