1975 Johnson 4HP 4R75, 4W75 Outboards Service Manual, Page 30Get this manual
CLEANING, INSPECTION, AND REPAIR SPARK PLUGS Inspect plugs for cracked porcelain and worn electrodesClean the electrodes with point fileAdjust gap to the specified .030 inchIn re- gapping, adjust only the ground electrode, as attempting to bend the center electrode will crack the insulatorSee Figure 4-7Poor motor performance and premature spark plug failure may result from improper spark plug installationBefore installing the plug, be sure the plug seat in the cylinder head is clean and free from obstructionsSee Figure 4-8Screw the plug in by hand, then tighten to the specified 17-1 to 20-1 foot pounds1654
Figure 4-8Cleaning Spark Plug Seat
If threads are stripped in cylinder head, Heli- coil
inserts are availableCaution should be taken when installing Heli- coil insertsTools and inserts are available from your parts distributorCLEANING BREAKER POINTS aAfter extensive service, the breaker points may become worn, dirty, or out of adjustmentInspect the breaker assemblies for corrosion or unusual wearQuestionable breaker points should be replacedCheck action of the spring and free movement of the breaker armDo not change breaker arm spring tensionbDirt, foreign particles, and oil are very detrimental to contact performanceThe oils and acids from person's hand, even though clean, can affect contact resistance, Oil deposits on the paints will cause them to burn out after very short period of operationNEVER FILE POINTS - repla ce themc To remove any traces of dirt from contacts, insert strip of bias tape dipped in alcohol or trichlorethylene and work it up and down between the paintsRepeat entire cleaning procedure for second set of pOints