Re: 1968 65hp Johnson Spark Plug
Richard.... That V4 1968 65hp Johnson originally started out using Champion L19V spark plugs, then eventually upgraded to Champion L77V (higher heat range) plugs, both of which are what is called Surface Gap plugs meaning there is no gap to set.<br /><br />Shortly thereafter a UL77V plug was introduced which was also used. The "U" indicated a supressor type plug which was designed to eliminate any ignition/electrical interference that might affect the electronic equipment on the boat.<br /><br />However, the surface gap plugs as listed above, regardless of their designated heat range were a cold running plug and would not operate properly on all engines.... even identical engines (No, I don't know the reason why).<br /><br />The cure was to install a spark plug that had a absolute heat range and could be gapped. The Champion L77J4 and later a L77JC4 came into existence and did the job nicely. There is also a UL77J4 and a UL77JC4 plug (The "U" description as stated above).<br /><br />Bottom line.... Your engine (1968 V4 65hp) has what is called Battery Capacitance Discharge ingition and incorporates a distributor cap and rotor. The proper spark plug would be any of the above. Personally, I'd use either the L77JC4 or the UL77JC4, and in your case set the gap to .030.<br /><br />The .030 gap is used as the spark needs to jump a extra gap at the rotor/dist cap area.<br /><br />- - - - - - - - - - <br /><br />For the others that might be reading this, the ignition system that came into being in 1973 is called Magneto Capacitance Discharge, it utilizes no distributor cap and the gap is increased to .040 . However, that gap had changed again at some point in the very late 1990's for some reason.
