1991 Johnson/Evinrude Models "EI" 40 thru 55 Service Manual, Page 117Get this manual
RPM Limiting Ignition Module This ignition module has 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 40-55 RPM Limit 6100
CD2UL Ignition, General Information
Troubleshooting the Ignition System