Arrghhh, Chinese kits! I've built one set with Litetek's Viton - perfects. The jet block seal on any other kit just won't last (but if you ask @blair nicely, he'll sell just those for those of us on tight budgets). And you'd think their fatter merge bung ring is better, but sitting carbs over paper a tiny weep was apparent. It's soft, and nicked on insertion. A 7 X 1.5 from a seals shop fixed it.