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2 engines, different #s

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  • 2 engines, different #s

    The 31 has 2, 454s. Built buy the same shop at the same time. Both carbs were just redone by Hobbs and are identical. They both run great but the right hand engine burns more fuel than the left hand rotation engine. I think. Don't know if the tachs are right or the synchronizer or the flow scan. How would you run your boat. Engine synchronizer, tach or flow scan. Sync, the left hand engine is 400 RPM higher and 20% less fuel. Tach, the left hand engine is burning less fuel but is way over according to the engine sync. Line them up according to the flowscan and the left hand engine is 400 over the right hand engine in RPM and way over on the synchronizer. How the hell am I supposed to know what is going on?.
    1988 26' cuddy
    1975 20' open
    31 Grand Slam
    16' Sandpiper
    14' Certified Fiberglass

  • #2
    Is it possible that the wires are reversed for one of the engines on the sync?
    1990 26’ open 351W

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    • #3
      20% is a huge difference. I would be suspicious of the flow scan. Swap the sensors?
      Steve
      1998 260 Mackinaw Sea Maxx 5.7 HO TBI 12' Klamath w/ 20hp Tohatsu EFI

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      • #4
        Are the Tach's accurate thru out the rpm range not to each other but to an hand held Tach of some sort ? Are the main jets are identical in both carbs? Is one engine starting to get into the secondary's?
        Serenity
        07 246 WA
        5.7 MPI Crusader

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        • #5
          Carbs are identical. Same jets and metering rods. Don't know if it is getting into the secondaries, can't hear, but I don't think so. Fuel burn is different at all RPMs. Fuel totalizer is correct, I'll swap sensors. All new gauges, as is everything else in this boat, but I would bet the tachs are not correct. I'll hook up shop tachs. How does the synchronizer get its signal?
          1988 26' cuddy
          1975 20' open
          31 Grand Slam
          16' Sandpiper
          14' Certified Fiberglass

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          • #6
            I never had a synchronizer on my twins. I just went by feel, they make a rhythmic hum when not in sycnh. You can hear and feel them come into synch pretty easily if you're listening and when they get close, they seem to talk to each other and synch themselves. Try that and see how she runs, and get a hand held tach to check out each engine against your other gauges as mentioned above.

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            • #7
              Originally posted by Quik Fix View Post
              Carbs are identical. Same jets and metering rods. Don't know if it is getting into the secondaries, can't hear, but I don't think so. Fuel burn is different at all RPMs. Fuel totalizer is correct, I'll swap sensors. All new gauges, as is everything else in this boat, but I would bet the tachs are not correct. I'll hook up shop tachs. How does the synchronizer get its signal?
              If you are after the fuel reading Floscan are great but there no system is perfect, with that I have been thinkin of adding in line Flow Meter like we did on the commercial side, it will measure gpm but it will be below deck and not fancy but it did the job well on the duffy . For the RPMs plug a digit timing light .

              https://i.ebayimg.com/images/i/20201...-1/s-l1000.jpg
              Last edited by Windex; 06-18-2019, 04:36 PM.

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              • #8
                Props. Or drivetrain. Use a phototach and see what the RPM's are. You can even use it on the shafts.
                Last edited by Pedlyr; 06-18-2019, 05:30 PM.
                '78 20ft Cuddy
                Mercruiser 350 FWC preVortec w/Carb

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                • #9
                  I just saw the post on DEBF. I swear I read this first!
                  '78 20ft Cuddy
                  Mercruiser 350 FWC preVortec w/Carb

                  Comment


                  • #10
                    DEBF is a great forum, too bad those guys don't realize what a great bargain a Shamrock is.
                    1988 26' cuddy
                    1975 20' open
                    31 Grand Slam
                    16' Sandpiper
                    14' Certified Fiberglass

                    Comment


                    • #11
                      Originally posted by Quik Fix View Post
                      DEBF is a great forum, too bad those guys don't realize what a great bargain a Shamrock is.
                      Well a lot of those guys are PIA Yankees. But really they are much more serious about their boats for different reasons. Most here are in it more for an affordable hobby and more laid back
                      '78 20ft Cuddy
                      Mercruiser 350 FWC preVortec w/Carb

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                      • Fisherlady2
                        Fisherlady2 commented
                        Editing a comment
                        Be careful, I am one of those PIA yankees, but i am good for morale support and dessert baking! LOL

                    • #12
                      And we have one make, not hundreds. They know their inboard boats. Good source of info. Like everywhere else though, you have to weed through the "not so smart".
                      1988 26' cuddy
                      1975 20' open
                      31 Grand Slam
                      16' Sandpiper
                      14' Certified Fiberglass

                      Comment


                      • #13
                        I have a phototach,PM me an address if you want to try it.
                        Serenity
                        07 246 WA
                        5.7 MPI Crusader

                        Comment


                        • #14
                          Originally posted by redneck View Post
                          I have a phototach,PM me an address if you want to try it.
                          Thank you for the offer. I bought a cheap one today. Can't believe I didn't have one before this. I'll have to keep my eyes open for a deal on a good one.
                          1988 26' cuddy
                          1975 20' open
                          31 Grand Slam
                          16' Sandpiper
                          14' Certified Fiberglass

                          Comment


                          • #15
                            You have probably already addressed this, but I will offer my thoughts just in case they may help.

                            The flow sensors and displays typically have adjustable "k" factors that allow for accurately calibrating the flow rate and gallons burned. I have calibrated similar flow sensors after several fillups by comparing total gallons measured and actual gallons burned and adjusting the "k" factor. I suggest you determine if the "k" factors are equal. Then I would try to burn 50 to 100 gallons through each engine and determine if the flow measuring equipment accurate depicts the actual fuel burned. Once confident the flow sensors are accurately measuring the flow rates and totals, then focus on the engines etc...
                            Kingfisher
                            1990 22' PREDATOR INDMAR 5.7 310 HP and ZF 45 C
                            Fishineer
                            1976 20' CENTER CONSOLE Ford 302 and B/W 1:1
                            Wilmington, NC

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