Engine air admittance regulation system

An engine air-in control system is disclosed, which utilizes that an air-in control device is connected with a respiratory flexible pipe of the engine, and is used for sucking air leakage of the respiratory flexible pipe of the engine to mix with outer gas, and then the mixed gas is sent to the engine to rekindle, wherein the air-in control device is provided with a pressure induction valve, a suction port, a core vent and a pore which is connected with sub-atmospheric pressure, wherein the core vent and the pore which is connected with sub-atmospheric pressure are directly or indirectly communicated with an air inlet of the engine to produce pressure difference change by utilizing the change of the air-in speed of the engine in order to close or change the opening amplitude of the pressure induction valve, the better air-in control device is provided with an adjusting button which controls opening limiting of the valve and enables the air-in control device to be suitable for the engine air-in control with va