On my single carb, fuel overflows from there when float gets stuck. I thought perhaps there was meant to be a pipe to direct such erroneous overflow to ground and avoid the hot bits, but it appears not. I had overflow pipes on my old MG, but have not worried too much now since fuel did not combust on exhaust manifold, but did stink, quickly warning me of the situation. And cleaning that side of the engine! If indeed that's a similar d shaped hole as on the sc. If not, apologies for spouting nonsense in addition to petrol!