This is a dismantled fuel tap. Two common causes for a leak here are the fuel tap o-ring approx. size 19mm x 2mm and the rubber washer approx. size 20mm (o.d.) x 12mm (i.d.) x 2.5mm (thick). The latter forms part of the strainer set 16952-341-671, the o-ring is not listed by Honda but try a plumbers merchant for both of these.