The most delicate part in a CV carburetor is the vacuum valve. Your carburetor will hardly work when this rubber membrane is punctured or torn. Harley-Davidson only sells the vacuum valve installed on the throttle slide (OEM 27585-88), but we have just the rubber available for a much more economical price. Fits all stock Keihin CV carburetors as found on all 1988 thru 2006 Sportsters, 1990 thru 1999 Big Twins and 1999 thru 2006 Twin Cam models.