Abstract: One embodiment of a device and method for controlling or restricting the air-fuel mixture into an internal combustion engine having a body member rigidly mounted between the air-fuel metering device and the engine intake, a slidably insertable restrictor plate, and a retaining and sealing cover. The body member may contain a single spacer or two spacers and may contain either a slot or a groove that communicates with the plate. The plate may contain a plurality of bore holes and multiple distinct plates can be made in order to achieve various and linear amounts of restriction. The plate can be easily and quickly changed depending on the amount of restriction desired. One or more embodiments of the device can be used on engines in various motorized vehicles and in various motorsports, such as drag racing. Other embodiments are described and shown.