My F1 has an F2 tank, the only difference between the two tanks is that the petrol tap spigot is a different size and therefore the tap is different as well, as I am finding out the F1/F2 tank is very small and is a pain. The following is from the handbook, the fuel tank holds 3.7 imp gallon capacity (17 liters, including 5 liters reserve which is 1.1 imp. gallon).
As far as I know they are the only tanks that fit the F1 apart from aftermarket ones. A 5 gallon version would be a load better.
Cheers
Den