Could it be for making a 'T' run on kerosene? Back then kerosene was cheaper than gasoline and many farm tractors had a "hot manifold" (exhaust jacket around the intake) to vaporize the kerosene which is more like diesel fuel than gasoline. Tractors had a small tank for gasoline for starting and warm-up before it would run on kerosene. Dad used to tell about how they would plow for several days on kerosene and then carbon would build up so much the exhaust valves would not seal so they'd run a few tanks of gasoline until the valves "healed up", as he put it. Also,not all the kerosene would vaporize and would get past the rings into the oil and dilute it. The oil level would actually increase and there was a petcock on the side of the oil pan that you opened every morning to drain off the kerosene (it was lighter than the oil so rose to the surface overnight). After the Depression most farmers installed what they called a "cold manifold" to run just gasoline, which gave more power and obviously burned cleaner.