I have a 1975 9.9 which is used as a sailboat auxiliary. It is a long shaft electric start and has the workboat prop (10 x 5) and reverse thrust kit. Since new it has been bad about fouling plugs. The only solution I ever found was to use ONLY Johnson 2 cylinder oil. Recently it doesn't seem to matter what oil or plugs I use, plugs still foul.
Some time I ago I rebuilt the power head including a new reed valve and cylinder head. Looking into the spark plug holes it appears that the head is ported, i.e. the sparkplug opening into the cylinder has a half-dome over the tip that is only open on one side. It would seem to matter where the ground electrode is with respect to that opening, but there is no way to control that. I have read about automotive power engine builders "indexing" plugs with washer shims to get the electrodes aligned.
The original plug was L7J. Then I think UL88C was recommended, but Champion's web site says that Johnson recommends only Q series plugs or misfiring may result. Recently I have seen NGKs recommended.
Questions:
1. Should I be indexing the plugs? Neither the head threads or the NGK plugs are repeatable, i.e. different plugs in the same cylinder don't torque to the same alignment. Neither does the same plug in different cylinders. What is more important, the alignment or the "reach"?
2. What plug should I be using? I haven't found one yet that doesn't foul pretty quickly.
3. Any suggestions on oil to minimize fouling?
Thanks,
Al
Some time I ago I rebuilt the power head including a new reed valve and cylinder head. Looking into the spark plug holes it appears that the head is ported, i.e. the sparkplug opening into the cylinder has a half-dome over the tip that is only open on one side. It would seem to matter where the ground electrode is with respect to that opening, but there is no way to control that. I have read about automotive power engine builders "indexing" plugs with washer shims to get the electrodes aligned.
The original plug was L7J. Then I think UL88C was recommended, but Champion's web site says that Johnson recommends only Q series plugs or misfiring may result. Recently I have seen NGKs recommended.
Questions:
1. Should I be indexing the plugs? Neither the head threads or the NGK plugs are repeatable, i.e. different plugs in the same cylinder don't torque to the same alignment. Neither does the same plug in different cylinders. What is more important, the alignment or the "reach"?
2. What plug should I be using? I haven't found one yet that doesn't foul pretty quickly.
3. Any suggestions on oil to minimize fouling?
Thanks,
Al