Johnson Evinrude Outboard Motors 1956-1970 1.5-40hp repair manual., Page 46Get this manual
POWERHEAO the engine begins to run too hotThe light on the dash can be checked by turning the ignition switch to the ON position, and then ground the wire to the sending unitThe light should come onIf it does not, replace the bulb and repeat the test3-5 REED SERVICE
Many, but not all, heads have thermostat installedIn addition to the thermostat, the engine may have thermostat bypass valveThese two items are easily removed, inspected and cleanedNormally, if thermostat is not functioning properly, it is almost always stuck in the open positionAn engine operating at too low temperature is almost as much problem as an engine running too hotTherefore, during major overhaul, good shop practice dictates to replace the thermostat and eliminate this area as possible problem at later dateLay piece of fine sandpaper or emory paper on flat surface (such as piece of glass) with the abrasive side facing upWith the machined face of the head on the sandpaper, move the head in circular motion to dress the surfaceThis procedure will also indicate any "high" or "low" spotsCheck the spark plug openings to be sure the threads are not damagedMost marine dealers can insert heli-co il into spark plug opening if the threads have been damagedOn many engines, sending unit is installed in the head to warn the operator if