This air cleaner mounting kit was designed to provide an alternative choice to those of you with a HS40 Mikuni SmoothBore carburetor on your Evolution motor. This kit allows to mount any of our air cleaners to the Mikuni HS40 carburetor. The adaptor ring is a light pressfit over the bellmouth of the carburetor and is held in place with three screws. Fits Evolution Big Twin 1984-1991 and Evolution Sportster 1986-1990 with a Mikuni SmoothBore carburetor.