Some time between 1915 and 1920 the quality of gasoline (petrol) changed. From the period literature - pre ethyl - gasoline - the by-product of kerosene production was a purer lighter gasoline. There was less kerosene in the gasoline. The period text describes it as going from a lighter gasoline to a heavier gasoline - more by-products of kerosene in the mix. Has any one found modified carburetors that were machined to accept the new gasoline blend? From a 1921 text there is a description of a modified Holley carburetor. This modification was accomplished by opening up the mixing tube from 13/16 inch to 23/32 inch. This machining was to allow the newer and heavier gasoline to mix with air better for better mileage and power.
I believe light gasoline is described as light naphtha.
I have a double fuel carb manifold made for running gas/kero in my collection.It is a Holley.
I believe the dual fuel carburetor came into manufacturing existence after 1919. This would be after the quality of gasoline changed.