introduced just up stream from the intake valve in the inlet port in each individual cylinder head in the direct fuel injection system, as opposed to the pressure carburetor where the fuel is introduced at the carburetor. These fuel control devices were individually sized and calibrated to fit almost all piston aircraft engines used by both civil and allied military aircraft made in the post war era. These fuel injection systems are found on high performance general aviation piston engines that continue flying into the 21st century. Design and development Starting with the basics of fuel combustion, no matter what type of fuel system is used on a given engine, the carburetor's sole job is to provide exactly the correct amount of fuel into a given amount of air that is entering the engine. To be burnable, the air to fuel ratio must be within the flammability limits of between of air to of fuel (for gasoline engines). Above or below this ratio, the fuel will not burn. Next, it is also a given that within that range of acceptable mixtures, there is only one ratio that is the ideal air-fuel ratio at that time, given the throttle position set by the pilot. In summary, it can be said that the ideal carburetor provides the correct air-fuel mixture ratio, as required by the engine, under all of its operating conditions. Lastly, the exact amount of fuel needed changes between the overly-lean lower limit of 16:1 and the overly-rich upper limit of 9:1 as the engine operating condition changes. To summarize, for a carburetor to deliver the exact amount of fuel required, it is necessary to provide the carburetor with three things: First, the exact weight of the air flowing through it, Second, what air-fuel ratio is needed for the engine's operating condition, Third, what engine operation is sought by the aircraft's pilot. Once these three things are delivered to the carburetor, a well designed carburetor will provide the engine with the exact, correct, fuel flow at all times. Any well-designed carburetor does this routinely, no matter what type or size engine is used. Aircraft carburetors on the other hand, operate under extraordinary conditions, including violent maneuvers in three dimensions, sometimes all at the same time. The problems: ice, gravity and inertia When fuel is vaporized, it cools the surrounding air due to the refrigeration effect as the fuel absorbs heat