Hi Michael
All my 2.3/4hp models from 1910 to 1925 have 1/4" copper pipes (nickel plated) for both petrol and oil pipes. The standard connector at the base of the carburettor, Douglas or AMAC, would be large enough for a 5/16" pipe but I doubt that the usual petrol taps available that only have a 1/8" BSP thread into the petrol tank would have a bottom union nut large enough to take 5/16" pipe. I cannot guarantee that some models may not have had 5/16" petrol pipes originally as these are fairly fragile items and together with petrol taps may have been replaced several times over their lifetime. Chris.
