Engine overspeed control circuit with defeat detection

Overspeed control circuitry for an internal combustion engine, comprising:

• tachometer means outputting a voltage as a function of engine speed;
• reference voltage means;
• comparator means having a first input coupled to said tachometer means and a second input coupled to said reference voltage means and outputting a disable signal when the tachometer voltage increases above a given value relative to the reference voltage to disable the engine and prevent running of the engine above a given speed;
• fuse means connected in circuit with one of said inputs of said comparator means, said fuse means having a normally closed-circuit condition providing a first impedance at said one input such that the engine is prevented from running above said given speed;
• terminal means enabling the engine operator to apply a voltage to said fuse means to blow said fuse means to a permanent open-circuit condition providing a second impedance at said one input such that said tachometer voltage can increase above said given value without said comparator means outputting said disable signal, to permit running of the engine above said given speed.