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Mercruiser 3.0 - runs great, but won't restart

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  • Mercruiser 3.0 - runs great, but won't restart

    Here is my situation:

    I when cold - I can get my boat to start, and it will run great. all gauges indicate normal . after 15 minutes at idle, if i turn it off and wait 1 minute, it will not restart, needs a significant cooling period.

    at this time i look in the carb and i see water droplets on the throttle plates???
    is this normal?????

    I'm guessing I have a crack in the manifold, which is letting water in to the intake and condensing on the throttle plates. Is this a a good guess??


    Here is my setup:

    1989 Mercruiser 3.0L
    petronix ignition
    new fuel, filters,etc.

  • #2
    Re: Mercruiser 3.0 - runs great, but won't restart

    Did you bypass the ballast resistor or the resistor wires in the circuit when you installed the Pertronix? Did you put on a non-resistor type coil? That usually helps the situation you're describing. The original coil uses a resistor that adds resistance to the circuit as it heats up. The Pertronix system doesn't work well with this setup.

    I don't know about the droplets. Are you sure they're water? Could it be gas? Sometimes the air flow through the carb can cause condensation, since that part of the engine is colder than the rest. I can't imagine that the water would find its way from the exhaust manifold into the cylinders, through the intake valves, back up into the carb and onto the throttle plates without causing some other far more serious problems than just hard starting.


    • #3
      Re: Mercruiser 3.0 - runs great, but won't restart

      thanks -

      i have had this issue on and off for years. worse this year.
      in the past i have gone back to points and rotor with no change.
      different coils etc.

      fuel is new

      it is water on the plates because it beads up, i don't think fuel would do that?

      intake and exhaust share the manifold, so water could pass diretly thru a crack and into the intake?


      • #4
        Re: Mercruiser 3.0 - runs great, but won't restart

        I have three friends with the same motor, all with the same problem. All are well tuned. All are Rochester carbs. I have no idea what makes this happen, but at least you know you're not alone.

        You say you've switched coils around. You need to go over to a known good non-resistor type coil. Otherwise, you may have multiple causes for the same problem. Take power to the coil directly from the starter solenoid's small positive terminal. That will rule out the coil. It has to be either not enough spark, not enough gas, or too much gas. Each of these has its own symptoms.

        I'd check the plugs for fouling first. Figure out what's happening inside of those cylinders when it won't start. Is there condensation on the plugs? Black residue? Reading the plugs will tell you a lot about what's wrong.


        • #5
          Re: Mercruiser 3.0 - runs great, but won't restart

          cheburashka -

          the plug I removed today is dry and looks perfect to me.

          thanks for your suggestions.
          i'm pretty much at the end of the line with this thing - if it wasn't for the kids i would have rid myself of it long ago.

          i bought this boat 10 years ago - it was well cared for, and for the first 2-3 years i owned it - not a bit of trouble.

          then this problem started - i replaced EVERYTHING (wires, cap, carb, plugs) and eventually added the pertronix.

          it used to have 2 issues 1) it would sputter and die after warm up. 2) the restart problem. it would ALWAYS restart after sitting for a while, now that does not seem to be the case - i really have to mess with it to get it to go.

          one last thing that doesn't make sense but i'll throw it out there anyway:
          as i'm cranking it is more likely to start just as i let off the key and the starter is disengaging????

          again - thanks for your suggestions.


          • #6
            Re: Mercruiser 3.0 - runs great, but won't restart

            Sounds like your vaporizing the fuel. Bad fuel pump or line close to heat. I'm more of a car guy but that's what it sounds like. Sometimes in a car the intake will get so hot it boils the fuel out of the fuel bowl and you have to put a spacer between the intake and the carb.

            You have spark when it won't start? You have good compression?


            • #7
              Re: Mercruiser 3.0 - runs great, but won't restart

              thanks -

              i have spark -

              not a vapor problem - all kinds of fuel squirting when i pump the throttle

              have not checked compression


              • #8
                Re: Mercruiser 3.0 - runs great, but won't restart

                My dad used to say motors are like a three legged chair. one leg is fuel, one leg is spark, one is compression. You have two.

                You could do a vacuum test too. You stated your plugs were dry so maybe the problem is between the carb and the intake.

                Keep us posted as I have a 3.0L with some carb issues as well not as bad.


                • #9
                  Re: Mercruiser 3.0 - runs great, but won't restart

                  What's your starting procedure for hot starts? When cold, my Pertronix-equipped 3.0 will rev up with a couple of second of cranking. when hot, it needs three pumps of the throttle and at least five seconds of cranking with the throttle wide open to starts. It acts like a flooded condition. I've seen several 3.0s with and without Pertronix which act the same way. I got tired of trying to trace the problem and learned to deal with it. When you say it won't start, what have you tried to make it start when hot?


                  • #10
                    Re: Mercruiser 3.0 - runs great, but won't restart

                    i've tried everything, wot, a few pumps, crank starter for 5 seconds, 8 seconds, 2 seconds.

                    After much thought - I believe your assessment of "not enough spark" is a correct one.
                    I've been spending a lot of time on this and concentrating on the fuel side - especially since ethanol was added to the equation.

                    My belief now is that it is an ignition problem. When the starter is cranking the motor - the batt voltage drops significantly due to the high current load of the starter. I think this reduced voltage to the hot coil/Pertronix is providing insufficient spark. If this is accurate I should be able to prove it very easily by providing the ignition with it's own power source.

                    I started thinking back to when it starts after warming up - and i realized that sometimes it will fire up just as I'm "giving up". By "giving up" I mean when I stop turning the key with the starter disengaging, but the motor still with 1/2 revolution - it sometimes fires. Under this condition, the bat voltage is returning to "normal" as the starter load is being removed and therefore there is higher voltage to the coil, which will create a stronger spark. once it starts it runs great because the coil voltage is back to 13-14V

                    Can't get back to it for a few weeks as it's no longer in the driveway but at it's summer resting spot on Cape Cod.

                    once again - thanks for your suggestions and ideas - i'll post my results in a few weeks.


                    • #11
                      Re: Mercruiser 3.0 - runs great, but won't restart

                      it is water on the plates because it beads up, i don't think fuel would do that?
                      Sounds to me like you have water in your fuel. Since fuel floats on top of the water, the pickup in the gas tank picks up water first, not gas. You need to drain the water out of the tank, probably pull the carb and clean it out also.

                      They don't run on water.
                      Don S.

                      Please, no PM's (Private Messages) regarding boat/engine problems.
                      That is what the forums are for.
                      Only forum/moderator issues will be answered in PM's.


                      • #12
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                        Re: Mercruiser 3.0 - runs great, but won't restart

                        drained fuel line, fuel pump and carb
                        fresh fuel tank (external).
                        new fuel
                        new water separator filter.