Carburetors: OEM as supplied from the engine manufacturer. Throttle shaft, butterfly and butterfly screw must remain stock. Surface finish of venturi and bore must remain as manufactured. All dimensions shown in PDF apply, no additional machining permitted. The color of diaphragms and gaskets is non-tech so long as the dimensions defined in the PDF fiche are observed. Auxiliary return spring is required for all butterfly type carbs. Carburetor may be run with the pumper stack on top or bottom.