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2750 5.7 merc rpms?-gctid368436

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  • 2750 5.7 merc rpms?-gctid368436

    First sea trial ever! Went great and everthing worked as it should. Curious what my WOT should be? I was at 4200, tabs up ...should i change prop for higher rpms? It sounded like it wasnt wide open to me... felt like i had more... i realize this isnt a speed boat but, i had more there IMO. Any help..

  • #2
    Did you trim the motor up for optimium speed? It normally will give you another 4-500 RPM and a couple more MPH...


    • #3
      Spec is 4200-4600 RPM's for the 1979 Merc 5.7. Maybe move down 1 pitch to get right in the middle of the band.
      Phil, Vicky, Ashleigh & Sydney
      1998 3055 Ciera
      (yes, a 1998)
      Previous boat: 1993 3055
      Dream boat: 70' Azimut or Astondoa 72
      Sea Doo XP
      Sea Doo GTI SE
      Life is short. Boats are cool.
      The family that plays together stays together.
      Vice Commodore: Bellevue Yacht Club


      • #4
        Abigayle III wrote:
        Did you trim the motor up for optimium speed? It normally will give you another 4-500 RPM and a couple more MPH...
        Having a lil trouble w the trim/tilt controls... our old speed boat has a simple trim up or trim down, this one has a 3 button control. up, down, in/out or something to that effect. Trouble is i cant see wut the drive is doin and what combination i need or what the hell any of this means! The PO said he always pushed the middle button along w the top button... please help i may move this to the tech forum as well.


        • #5
          Bottom button is "drive in", middle button is "drive out", top button is for "trailer" and is pressed with the middle button to put the drive all the way up for trailering.

          You should only have to use the bottom and middle button to trim - BUT if the trailer sending units are out of adjustment then you may have to use the middle and top to get it to trim out.

          Were you at WOT when you checked rpm's?

          Sounds like you did not go to WOT so you need to - then check your WOT. As said you need to be 4200 to 4600 rpm.

          Also do you have trim tabs? These 2750's benefit greatly from tabs.


          • #6
            Ill try it again when down there. The throttle was "smashed" to the dash! The boat came with 1/4 tank of fuel (pretty sure i paid for it, haha), so no problem burning it! I just now understand trim controls, so now ill have to play w that a bit. It just feels a$$ heavy... trim tabs down til plane, then up. So something to look at this weekend. It just didnt wind out like a motor should, maybe i should change the prop... or just keep it stock this year and feel it out.


            • #7
              An another note, from about 3/4 throttle to WOT it didnt sound much if any different. Ive played w engines my whole life, i choose to listen more-so than rely solely on gauges... thats just me


              • #8
                Maybe the butterfly did not open all the way. Maybe a simple adjustment on the throttle cable at the carb.

                Have someone else drive while you fiddle with the carb.
                Be good, be happy, for tomorrow is promised to no man !

                1994 2452, 5.0l, Alpha gen. 2 drive. Sold ! Sold ! Sold !

                '86 / 19' Citation cuddy, Merc. 3.0L / 140 hp 86' , stringer drive. Sold ! Sold ! Sold !

                Manalapan N.J


                • #9
                  To maximize the performance of your Victoria you will need to trim the drive up a few degrees, as already suggested, but you will also need the trim tabs down a bit to give the boat the lift it needs aft. A lot of things can impact performance and all should be considered before changing props. Engine tune and engine HP (what's a compression test telling you) as well as condition of the hull bottom are just a few. The 4200-4600 RPM someone mentioned earlier is correct but Mercruiser wants these things to run more near the 4600 RPM rather than the 4200 RPM rating. Testing should be with full fuel and water and an average load aboard the boat. With only 1/4 tank of fuel aboard you will probably find you're further off your RPMs than you think. Top things off and run it again with the drive trimmed a bit and a small amount of trim tabs. Over-propped and you run the risk of engine valve damage (Tuliped Valves) so make sure you get it dialed in.


                  • #10
                    Will do guys! Thanks for the input and advice!