1990 Johnson Evinrude "ES" 9.9 thru 30 Service Manual, P/N 507871, Page 110Get this manual
RPM Limiting Ignition Module Some ignition modules have built-in RPM limiting deviceCertain models are equipped with limiting ignition module to guard against possible powerhead failures caused by improper propeller selection (underpropping), excessive wear on propeller blades, improper motor installation, propeller ventilation, or unusually light boat loadingBe sure to use the correct ignition module when servicing the models listed below to control the engine's operating RPM range and protect it from possible powerhead damageModel
RPM Limit