Abstract: There is disclosed an engine additive supply and control device, for supplying a fuel supplement in small amounts which will have many desirable effects on operation of the vehicle or apparatus which is being driven by an engine to which the additive is being supplied along with the fuel and air mixture, the quantity of supply being controlled in response to manifold vacuum conditions and flow of additive through the device being controlled by passage way, opening and fluid line sizes, in the device, which are coordinated to prevent surging, flooding and to minimize consumption, while providing adequate quantities to produce the desired interaction with the fuel/air mixture, a container, a body with suitable wells and passages and interconnections being provided.