REBUILD KIT, CARBURETOR, MIKUNI BST40. Full list of parts contained in the kit: Float needle seat o-ring, cold start enrichment feed pipe o-ring, slide guide o-ring, two felt throttle shaft seals, two stainless steel flat hexalobular throttle blade screws, Japanese-made float needle & pilot screw o-ring, genuine Mikuni float bowl gasket & cold start plunger retainer to cable seal and instructions. All o-rings in this kit are FKM. NBR vs. FKM o-rings