a device for aiding in the control of the fuel - air mixture in an internal combustion engine having an accelerator linked mechanically to a carburetor and a ventilation passage from the crankcase of said engine to the intake manifold , said device comprising a valve housing having a seat coupled to an air passage adapted to communicate between outside ambient air and the ventilation passage ; a valve means for seating in the seat in the valve housing to prevent ambient air from flowing into the air passage , and a rotatable valve control cam means coupled to the accelerator to gradually open and close the valve as the accelerator is depressed . this device is used to increase the air in the fuel mixture so as to provide a more complete combustion .