Re: 1975 Johnson 135 No spark starboard side

[Don]

The sensors are in the timer base.
But again, I want to re-emphasize Dan’s point about these early engines and cranking speed. It is not uncommon for only two sensors to fire while cranking, then once the engine fires and RPM picks up, the other two sensors kick in. Later, updated sensors had improved windings and were a little closer to the flywheel hub magnet. So, if my crude methods point to the sensors, then go ahead and measure sensor resistances. Replace the expensive sensors if and only if the offending sensor resistance is way off/shorted/open.
What I am trying hard to avoid is you spending bucks for new sensors (timer base), getting spark on all four while cranking, but still having the engine problem that prompted all this testing…So, again I will ask just what prompted you to check spark. Is this engine new to you? Have you had it running yet? Were you just doing basic tests to evaluate the engine? Or, is there an actual running/starting issue.
So, if you have never had this engine running, I would go ahead and try to start it, perhaps the other sensor will kick in once the engine fires. This engine is an old 135hp, had lots of compression, detonation/preignition damage is not uncommon. Please inspect it carefully, starting with a compression test. I would also try to sneak a look inside the plug holes with a bore scope if you can get your hands on one. I have seen good compression readings even with partially melted piston domes or broken top rings.
Again, I am being cautious here because I don’t want to see you spend money needlessly, or on an engine with internal problems….D
PS- Dan’s point about the early stators (name of assembly that holds the charge coil and alternator windings) is valid as well. Even though the charge coil/stator may not be an issue now, it should be closely examined. The early ones had a tendency to heat up and melt down, you could usually spot a puddle of dark greenish hard goo that had dripped down off the charge coil and on to the block. So, if the original stator/charge coil is still in place, you should plan on replacing that as well. Don’t worry about this unless it is determined that you need to dig into/replace those sensors. Dan said he found a nice used stator for you on ebay.