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