Engine don’t immediately stop

KOHLER 9EKZOD, 4 strokes, Three-cylinder engine, pump/injector BOSCH 235-4 I have encountered a problem when tried to stop my KOHLER generator and it did not stop immediately, but kept cranking for some time. Shit I thought, what is that! Started again, stopped again, but it kept cranking for a while. First thing I have checked was a magnetic solenoid valve at fuel inlet line in case it stuck or was contaminated with anything from the fuel supply system. Didn’t find anything. Could it be a leaking injector? Unlikely, because engine was quite new and running stable. Eventually I came to fuel dumping line and question was, where is a non-return valve what should stop fuel being sucked back in pump/injector? So, how it turned out every injector has had own non-return valve. After tests and checks one non-return valve was found to be defective. The valve itself is very basic, there is a ball bearing ball inside, which is not spring loaded and shut the fuel line by gravity force when STOP function is activated.