Instead of trying to make an air-tight piston ... the pin pushes open a ball which acts as the inlet valve to pressurize an intermediate chamber. As the piston retracts, the ball closes the ...

the choke valve, operated manually or automatically, closes the carburetor's air intake to maximize the fuel content of the air-fuel mixture delivered to the combustion chamber inside the engine.

The valve consists of two chambers separated by a piston and a spring. The crankcase pressure is drawn from the crankcase via ...