I've got a mid to late 80s Mercury 70hp outboard with a jet unit on it that has developed a bit if a problem this past weekend that is eluding me a little so I'm looking to bump heads together and atleast give me somewhere to start. Just in the past two days I have developed a problem of where I start my boat, I'll make an initial run (my wife won't go unless I do) but when I shut it off it will not start for anything unless it has set for hours on end. I took it out te day after the problem first presented itself and I had a slightly difficult time getting it started but once I did it idled a little rough until I opened it up and let it run, then it ran and idled fine, but when I shut it off it wouldn't start again. I have checked a few things like making sure the tank is vented, there fuel/oil mix in the cylinders, it's got spark....Im just not a huge expert on marine power units so it's a little difficult for me to chase a problem I know little about (right now). I did notice yesterday though that my priming bulb when pumped will not stay stiff and seems to only hold fuel for a minute or two at best...I think replacing a check valve is in order however I don't think it is the single contributor to the entire problem.
I did make the mistake of putting premium in it the other day (which it has ran premium on occasion before) because I was filling up my car and I pushed the wrong durn button. I heard some crazy but reasonable theory that the premium will evaporate before ever making it to the cylinder, and to use a lower octane.
To me though it seems since I can get it running and it'll run fine initially that all of the obvious components are fine and evidently work properly....so now I'm kind of at a loss, don't know if it could just be sucking air somewhere or what