1990 Johnson Evinrude "ES" 40 thru 55, P/N 507872, Page 187Get this manual
& General Safety Warnings To avoid accidental starting of engine while servicing, twist and remove all spark plug leads When using shop air for cleaning or drying parts: aBe sure air supply is regulated to not more than 25 PSI (172 kPa)bBe sure you use appropriate eye protection to avoid personal injury Replace any locking fastener (locknut or patch screw) if its locking feature becomes weakDefinite resistance to tightening must be felt when reusing locking fastenerIf replacement is indicated, use only authorized replacement or equivalent Refer to Safety Section, Parts and B, for additional safety considerations