An adjustable restrictor device for controlling flow of induction air into an engine. The restrictor device may comprise a generally flat compact housing which is installed between a carburetor and intake manifold of an engine. The housing may have throughbores to allow air flow, which coincide in location to carburetor bores. The restrictor device may have two individual restrictors enclosed therein, each movable to positions which progressively obstruct and open the throughbores to control flow of inducted air. Each restrictor may be manually controlled in common by a rotatable control shaft. Threading of the knobs may be opposite handed, thereby enabling the restrictors to move similarly in effect as to controlling air flow but in opposite directions.