The game doesn't have it, this is because they have accurately modeled the Mk 2 spitfire and not stuck the Mk1 in with a pair of cannons
By the time of the Mk 2 they had identified this problem as the fuel was forced through by gravity not a pump. I believe tall they had to do was place a piece of mettle inside the eenginethat swivels and was weighted in a way that in negative 'G' it would swing down and stop fuel flowing backwards. Although i may be wrong on the solution bit
do correct me if i'm wrong!