Design
These were simple engines compared to modern engine design. However, they incorporated some very clever designs in several areas, many times because the designer was attempting to circumvent infringing a patent for a particular part of the engine. This is particularly true in the area of the governor. Governors were centrifugal, swinging arm, pivot arm, and many others. The actuator mechanism to govern speed was also varied depending on patents existing and the governor used. See, for example, U.S. Patents 543,157 from 1895 or 980,658 from 1911. However accomplished, the governor had one job - to control the speed of the engine. In modern engines, power output is controlled by throttling the flow of the air through the intake by means of a butterfly valve; the only exception to this being in diesels and Valvetronic petrol engines. On hit-and-miss engines, the governor holds the exhaust valve open whenever the engine is operating above its set speed, thus interrupting the Otto cycle firing mechanism.
The intake valve on hit-and-miss engines has no actuator. It has a light spring that holds it closed until it can be drawn open when a vacuum occurs in the cylinder. Such a vacuum can only occur when the piston is in a down-stroke and when the exhaust valve is closed. (Therefore, when the governor holds the exhaust valve open, the intake valve will not open.) This vacuum causes the intake valve to open, which allows the fuel-air mixture to enter.
Read more about this topic: Hit-and-miss Engine
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—Sidney Buchman (1902–1975)
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For Christ’s sake not black—
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—John Adams (1735–1826)