Abstract: An air injection device for attachment to the exhaust manifold of an internal combustion engine is described. A one-way or check valve permits air to be drawn into the air injector to the exhaust manifold when the pressure inside is less than atmospheric to allow more complete burn of unconsumed fuel. On the pressure stroke, the valve closes and prevents untreated exhaust gases from exiting the injector. The valve is designed with mechanisms, such as small protrusions, on the valve and/or on the seat or circumferences that the valve contacts to reduce or prevent sticking of the valve. In one embodiment, the valve may be spherical, and in another embodiment, the air injector may be provided with a mechanism to manually adjust the air flow through the injector.