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Thread: Won't restart

  1. #1

    Default Won't restart

    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

  2. #2

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    How long since you've changed the fuel filter? I have a line filter in addition to the one on the outboard, and I change them both annually. Dunno if that's your problem, but changing them would be my first step.

  3. #3
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    Throw that "theory" about premium out the window and forget you ever heard it-total rubbish.

    A bad check valve it may be, more likely suspect is a leaking connection(o-ring) at the motor, or fuel filter as BB stated. Another is a weak fuel pump. If you can, have someone squeeze the primer bulb continuously while you operate the boat, if the problem does not occur have them stop squeezing to see if it manifests, then repeat. Do it on a lake for safety sake .

  4. #4
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    My dads motor (mid 90s Mariner Jet - 40HP) had a similar issue which led to it not running at all. It was initially hard to start, but when it started, it ran good. Did this all day one day, and then after parking at the cabin overnight it wouldn't start the next day. It ended up being the stator (under the flywheel). Couple hundred bucks at the shop to get it fixed... They do wear out, so this is just another thought.... Hope you get it figured out.

  5. #5

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    Thanks for the help and input, sorry for not getting back on here to reply any sooner. The theory on premium I do agree sounds a little goofy, however in the Mercury Marine Maintenance manual for that specific motor has a dedicated section in it to this very issue, and this "theory" on using a higher octane fuel. Basically it says that once the chambers in the carb reach in excess of 200 degrees that it vaporizes the fuel, and when it is mixed with the air in the cylinder the mixture is too lean to combust. Again, I agree it does sound kind of goofy but Mercury has leant some credence to the theory.

    I have done a few things since then, more preventative measures or measures to treat the symptom until winter, then its going in the garage for a minor overhaul this winter. Fixing to go run it wither this afternoon or tomorrow and hopefully she'll scoot across the water, and restart on demand

  6. #6
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    Interesting, I had a 1992 Mercury/Mariner 55hp (2 stroke) I owned and ran on Premium fuel until 2010 when it I sold it in prefect running order. Regardless of what Mecury says, vaporizing the fuel is EXACTLY what is needed for optimal combustion, it is fact and is a major factor that led to the innovation of fuel injection. As long as the engine is running, new and cool fuel is being supplied to the carbs from the fuel tank preventing fuel boil. Now if Mercury is saying that a hot soak (engine of after running to operating temp)with premium fuel in the carb leads to Evaporation of the fuel in the bowls, then it is a design flaw in the carbs/manifold/airbox and not a direct result of the Premium fuel.

    Be sure to check for a good bright spark after every single time it will not start . The stator issue mentioned above is something to look out for.

  7. #7

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    @ .338 WM - Thanks for the tips and input, I can only relay what Mercury says in its manual but yes paraphrasing it it essentially says at around 200 degrees the fuel essentially boils, and once it does it becomes too lean when it mixes with air.

    Im shifting gears on this issue though because it is apparently obvious what this is now, and it is something within the ignition/electrical system. Went to Big Lake the other day and had an oil slick the size of Exxon Valdez when I was attempting to get it started because of a total failure of the electrical/ignition system. I drug it out of the water, and did what testing I could without the manual with me and I believe the either the stator but more likely the trigger assembly is bad. I seem to have very little to no spark on the #1 cylinder when it is hooked up correctly, when I swap the wires around the cylinder has plenty of spark, wish tells me for the most part everything back to the stator and/or trigger assembly is good. I have the troubleshooting tree and electrical schematics from Mercury, so as soon as I return from a college class I am going to burn the midnight oil and figure this out!

    Not being on the water is no fun.......

  8. #8
    Member DRIFTER_016's Avatar
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    First thing I would check is the CDI.
    This was the most common spark issue on that vintage of Mercs when we were using them up at the lodge I worked at.

  9. #9
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    I support .338 on his statements about premium. It seems like what you are stating is backwards. Maybe you are misreading it, or they misstated it in the manual, but premium stops predetonation instead of causing it. Back to your problem, it somewhat sounds like a vapor lock issue to me, or possibly a cracked fuel line or leaking clamp allowing air into the system causing a vapor lock. This may be a bit hard to see, since it would be sucking in air, and not necessarily leaking fuel. A cheap thing would be to replace all of your fuel lines with new hose, which may not be a bad preventive maintenance thing on an older motor anyways even if it turns out not to be the issue.
    2009 Seawolf 31'
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  10. #10

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    I don't think / know it is not a premium issue now, I dug thru the wiring diagrams and the technical section of the manual where it pertains to the electrical / ignition system, especially after Sunday's escapade of creating an oil slick on Big Lake (fuel coming from the exhaust port). Doing some troubleshooting indicated a lack of spark, shot the wires for the entire electrical/ignition system and it seems as if BOTH the stator and trigger assembly are bad. I think it is kind of odd, I am not sure how one directly affects the other but seems very odd both were to go bad almost at the same time. Pending replacement of those two items around the first of the month, had to order some parts and special tools for the job....just waiting their arrival!

  11. #11

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    Last year my 210 hp sportjet did the same thing this spring i was getting ready to troubleshoot the problem so i bought 2 new batteries and that fixed the problem. Evidently the ignition system does not like weak batteries.

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