Here is a close up cutout showing the check ball tube that protrudes into the gas tank of a Model Y
Briggs and Stratton engine. When the engine stopped running, (drawing in fuel) the check ball would
fall down into the base of the check valve tube shutting off the flow of fuel while the engine is not in
operation. This method was not unique to the engine world. It was a useful way to keep the fuel lines
from emptying back into the fuel tank when the engine was not in operation. This was particularly
helpful in applications where the gas tank was mounted below the mixer, (or carburetor) of an engine.