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  • Big vacuum leak?

    I winterized my boat last year and went to fire it up and now it is idling very rough, has trouble getting on plane, and will not reach faster than 40 mph or about 3500 RPM wide open.

    full tank marine stabile added last year before cover up ..A large rushing air sound. Feel sounds like a vacuum leak
    ran gr8 before fogging the carb and winterizing.
    . Where to start...Thanks again I-boaters.
    Last edited by Leaky Rear; July 4th, 2018, 02:18 PM.

  • #2
    what are you working on?

    the rushing air sound could simply be the intake noise as air rushes past the carb.

    is it running on all cylinders? did you foul plugs with your fogging oil. BTW, fogging usually fouls plugs

    is your fuel actually fuel or a mix of crud, water and fuel. check the contents of your filter.
    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

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    • #3
      the boat has been run on good gas. Ran perfect until I winterized.
      Would an hour of operation clear a foul plug?
      There is something missing ..When i plug a little hole with my finger it changes idle.

      Something around carb.

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      • #4
        Is the brass thing supposed to suck air?

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        • #5
          I will try replace fuel filter and check the plugs next day or 2 .

          Comment


          • #6
            Running a fouled plug doesnt un-foul a plug
            Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

            1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

            Past Boats
            1970 Wooster Hellion - Merc 9.8
            2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
            1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

            What’s behind you doesn’t matter.Enzo Ferrari

            Comment


            • #7
              When you winterized it, how long and at what speeds did you run it after you put in the fuel stabilizer?

              Don't worry about the brass fitting

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              • #8
                The hose coming from the rear of the carburetor , where does it go?
                Holleys should have the metering block gaskets replaced as the gaskets tend to shrink and various passages become blocked or will cause some to join together resulting in flooding and rough idle. Get a genuine Holley kit and rebuild the carburetor . They are not hard to rebuild.
                Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1

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                • #9
                  Originally posted by kenny nunez View Post
                  The hose coming from the rear of the carburetor , where does it go?
                  To a PCV valve. Volvo does use them

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                  • #10
                    I hope that is what it is as Mercruiser GMs use a hollowed out version. Worth checking that someone did not replaced it with a hollowed version.
                    Kenner, Louisiana 1980 Donzi 18'. 2+3 6.2 MPI Alpha 1

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                    • #11
                      Thanks forum members. Ive been caught up with work
                      , - will resume repairs on this when it cools off a bit here.


                      Had put the stabilizer in run not long at all - honestly- a few minutes tops.
                      Was added in at the dock and then winterized and covered and raised on the lift for the cold season.

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                      • #12
                        Pull the metering block off the carb and clean the passages, especially the power enrichment circuit(remove the power valve to access the orifices)

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                        • #13
                          Jimmbo - did see your post , been away . Gong to try the easiest first
                          ... Got back in the boat yesterday. Do not think I have a vacuum leak.
                          For the heck of it I rechecked all the spark plug boots - that they were on tight..

                          The rear cylinder at the driver's side- the spark plug seems to have stress on it , the loom and spark plug cable was pulled very tight. Plug tip broke off in my hand So I restarted on a hunch on 7 cylinders.
                          Ran exactly as it did with the "vacuum leak" I will go buy gap and install plugs today.


                          New problem also

                          Both water manifolds were HOT, and the pump at the bottom was cool , hoses from it were cool, and a big wad of black gunky grease under the pump. Has 4 flathead screws. Once a decade plus ago the plastic or rubber impellers fell off and the boat overheated . Got a hi decibel warning . Not this time. No reading on gauge. Pump , thermostat . I went through all this before but like I said a decade. So 2 problems , another failed raw water pump (looking at the owners manual from penta)
                          Last edited by Leaky Rear; December 3rd, 2018, 10:12 AM.

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                          • #14
                            I made progress on the operational issue. Replaced all the plugs with recommend on the Volvo Penta Manual .

                            Gapped at .035 and the motor idles like a kitten. I really do not think at this point there is a vacuum leak.
                            Id like to lake test but there is 10 minutes of slow water before I can plane on the Lake. Will overheat exhaust manifolds and risers . The hoses from the bottom pump are cold and feel empty.


                            So , in the slip with boat floating in the water...what might be best way to proceed to diagnose the overheating exhaust riser and exhaust manifolds. The exhaust risers look bloated.

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                            • #15
                              Sign up today
                              Got any pics of (bloated) exhaust risers? Thermostat good?

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