What action should you take if a runaway diesel occurs on a small engine?

In the event of a runaway diesel engine, the most effective action is to smother the intake. This is crucial because runaway diesel engines typically occur when the engine begins to run uncontrollably, often due to the engine ingesting its fuel uncontrollably, which can happen if there is a malfunction or failure in the fuel system.

By smothering the intake, you are cutting off the supply of air to the engine, which is necessary for combustion. Without air, the engine cannot continue to run, and this stops the runaway condition. This method effectively disables the combustion process and prevents further damage or danger associated with a runaway diesel.

Other actions, such as shutting off the battery or increasing throttle, would not resolve the situation and may worsen it. Opening the exhaust does not provide a practical solution either, as it does not address the intake issue that fuels the engine's runaway condition.