1978 Johnson 4HP outboards Service Manual, Page 15Get this manual
TUNE-UP PROCEDURE When an owner brings motor to you for tune-up, or for some minor operating malfunction, the following procedure should be used as guide to determine the cause of the malfunctionWrite down the owner's commentsKeep an accurate card file on your service shop operationEach service operation should be on record as to the: OWNER'S NAME DATE MODEL NOSERIAL NONATURE OF COMPLAINT NATURE OF WORK PERFORMED COST TO THE OWNER WAS WORK PERFORMED UNDER WARRANTY? After writing down the owner's comments, check the motor visually and begin systematic tune-up procedureConsult the Trouble Check Chart to find the causes of any malfunction which may be discovered when tuning up the motor1Remove exhaust cover and cylinder head Slowly rotate flywheel and visually inspect pistons, rings, and cylinders for wear, freeness, and carbon deposits
2Clean carbon from cylinder head and top of pistonsDo not alter piston deflectorSurface and reinstall cylinder head, using new gasket3I nspect spark plugsClean and regap or replace as necessary4Inspect and test sensor, coils and ignition wiresSee Section for test proceduresCheck for spark on each cylinder5Inspect carburetor and choke6Inspect fuel pump and filterReplace filter screen7Check throttle cam adjustmentSee Section