Replace your Mikuni carburetor o-rings with only genuine Mikuni parts.  The Mikuni 616-12001 main jet o-rings are made to higher standards and ensure only the best quality.  They are made from a rubber polymer that remains pliable even after many years of use and ensures an exact fit and proper function in all conditions.  This o-ring fits all Mikuni carburetors using the Mikuni N208.099 press fit main jets.  A highly typical application are the BDST38 OEM carburetors for Ducati and Yamaha but will fit any application using the N208.099 press fit main jets.  Mikuni OEM #616-12001.