Half full wing tank on the D.150= 4 gallons, enough for just under an hours flight. Of course, you would have had the aux fuel pump selected on as part of your HASELL checks wouldn't you? I would have used either tank in turn and balanced the fuel equally for the sortie, but hey, what do I know?
I still reckon the idle mixture is set incorrectly. That much smoke staining is not right, but hey, what do I know?
The pic was taken last weekend :-)