Some troubles that may cause an engine to hunt, or vary its rpm at constant throttle setting, are similar to those that may cause an engine to resist stopping. Generally, these two forms of irregular engine operation

Figure 3-40.Possible troubles that may cause an engine to stall frequently or to stop suddenly.

are caused by troubles originating in the speed control system and the fuel system.

Speed Control System

The speed control system of an internal-combustion engine includes those parts designed to maintain the engine speed at some exact value or between desired limits, regardless of changes in the load on the engine. Governors are provided to regulate fuel injection so the speed of the engine can be controlled as the load is applied. Governors also prevent overspeeding as may happen in rough seas when the load is suddenly reduced as the propellers leave the water.