Well, if it were me (I have been in your shoes with an outboard chasing gremlins around many times) I would start with a compression test, then do a compression leak down test and see what you have with the internals of the engine-- your findings will lead you in the direction you need to go to trouble shoot your issue. If the internals are healthy I would go to the ignition system and test everything per specs-- use a true shop manual that will go into great detail on every section of the outboard, however they are a bit vague about getting out v4 thermostat housing and install ect other than pulling the power head....I'm no professional mechanic and don't claim to be either. I have built many hot rods over the years and that knowledge help me when I work on my outboards