MERCRUISER HI-PERFORMANCE SERIES  No. 91-1


FIREPOWER IGNITION SYSTEM

Operation and Test Procedure

The Firepower ignition system uses the MerCruiser Thunderbolt IV distributor along with a Firepower ignition control box and coil.

The reason for using the Firepower control box is it has built in (soft touch) rev limiting capability. The rev limiter is set at 5400 RPM. When the engine reaches 5400 RPM, the control box causes the engine to misfire by masking out the spark on every fifth cylinder. The cylinder that is masked out will change each revolution of the engine until the engine RPM falls below 5400.

Because of the rev limiting capabilities on these engines, it is extremely important to prop the boat within the recommended operating range of the engine. If the boat is under-propped and the engine is allowed to bounce off of the rev limiter, the engine will fall off in power.

The rev limit RPM is pre-set at the factory and cannot be adjusted in the field. The rev limiter is installed to protect the engine when a boat becomes air born in rough water.

The Firepower ignition control box also controls the spark advance of the engine, much the same as the ignition amplifier does on the Thunderbolt IV ignition system.

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