Abstract: 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.