In automotive contexts, a choke valve is a valve that modifies the air pressure in the intake manifoldof an internal combustion engine,and thereby modifies scion xb the ratio of fuel and air quantity entering the engine. Choke valves are generally used in engines with carburetors,to supply a richer fuel mixture during engine start than at other times. Most choke valves in engines are actually butterfly valves that are mounted in the manifold above the carburetor jet, to produce a higher partial vacuum and thereby draw more fuel into the intake stream scion

• choke valve is sometimes installed in the carburetor of internal xb   combustion  engines.Its purpose is xb to restrict the flow of air, thereby enriching the fuel-air mixture while starting the engine. Depending on engine design and application, the valve can be activated manually by the operator of the xb  engine (via a lever or pull handle) or automatically by a temperature-sensitive mechanism called an auto choke.Choke valves are important for carbureted gasoline engines because small  xb droplets of gasoline do not evaporate well within a cold engine. By restricting the flow of air into the throat of the carburetor, the choke valve raises the level of vacuum inside the throat, which causes a proportionally greater amount of fuel to be sucked out of the main jet xb and into the combustion chamber during cold-running xb operation. Once the engine is warm (from combustion), opening the choke valve restores the carburetor to normal operation,xb  supplying fuel and air in the correct stoichiometric ratio for clean, efficient combustion.Chokes were nearly universal in automobiles until fuel injectionreplaced carburetion in the late 1980s. Choke valves are still extremely common in other internal-combustion applications, including most small portable engines, motorcycles, small prop-powered airplanes,and carbureted marine engines choke xb