Quote from Tractor Data
Known as tractor vapourising oil or distillate, this once-cheap fuel was commonly used in farm tractors until World War II. Many manufacturers built low-compression "all fuel" engines designed to burn tractor-fuel, gasoline, or kerosene. The engine was started on gasoline from a small tank, and switch to tractor-fuel once it was warm.
Tractor-fuel was a low grade fuel produced between gasoline and diesel in the traditional distillation of crude oil. The refining techniques developed during World War II made it possible to convert this into more useful fuels, and it began to disappear.
A tractor-fuel engine can be run on modern gasoline. The lowest grade of gasoline available today is often better than the highest grade available when these engines were built."