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Excessive fuel burn-gctid396009

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    Excessive fuel burn-gctid396009

    Quick question. We just started our 9-day boat vacation around the bay and was we were cruising down to Annapolis, I noticed that my starboard engine was burning a significant amount of fuel than the port engine. I think the numbers were something like 12-13 gph port to 16 gph starboard at 3600 rpm each as measured on my Twinscans. What should I be looking for when trying to find out why? The engines are 5.7L, 250 hp, carb'ed Mercruisers with Bravo IIs.

    My normal fuel burn is 20 gph, but with the discrepancy of burn between the engines, I burned 30 gph for the trip. That is a 50% increase and we still have a few more 2-3 hour runs for the rest of the vacation. Any ideas or suggestions would be greatly appreciated. Thanks in advance.

    I have had the problems twice...1st time was the ignition module...2nd time was the carb needed rebuilding
    1997 Bayliner Trophy 2352
    5.7 Mercruiser/Alpha I Gen II /Full Closed Cooling
    San Diego, CA

    HookEmDanO out ......

    the more people I meet the more I love my dogs !


      Pull the flame arrestor and inspect the function of the Choke. This is easy to do. Harder to spot is a heavy carb float. You can look down the carb sometimes and notice (during idle) a periodic flooding condition in the carb bore. This would indicate that the float is heavy and the carb is flooding.

      If your exhaust is out the transom, you can check for excess carbon in the exhaust tips.

      Sometimes you loose electricity to the electric choke. Check this with your meter or test light. My older boat had the electric choke hooked to the auxiliary connection at the alternator. The alternator was dead, so, the choke didn't open. It would open 5/8 of the way at high speed, but even this little restriction caused a huge fuel burn.

      Once in a great while, the floscan can be fooled by AIR BUBBLES in the fuel line or Cavitation air bubbles ahead of the flow sensor. Make sure the fuel line is straight before the flow sensor. (6" or so) There's a lot on this in the FloScan manual/web site.


        Thanks for ideas. The flow sensors have been installed for about 4 years now, but could still be the issue. I remember last weekend that starboard wasn't reading anything for a bit until I shut down the engine and restarted.

        I will know if he twinscans are accurate when I fill up the tank Monday. If the accumulator is accurate, then it's time to look at the choke or carb.

        Thanks again and if anyone else has something, please chime in.


          Randy, during vacation may not be the time to try this, but with twin engines, we always have the option of swapping suspect components to the other engine.

          An easy and quick one, would be to swap flow meter sensors. These are identical, and will swap easily.

          If the heavy usage now shows up on the Port engine, you'll know that the sensors are not reading the same.

          However, since you believe that your fuel burn has increased, this is not a likely suspect.

          Next may be carburetors. You'll need a set of base gaskets for this swap.

          If the heavy usage now shows up on the Port engine.............. yada yada yada.

          Next may be ignition modules. These too are identical, and should swap easily without any parts.

          Same as above, if the heavy usage now shows up on Port....... yada yada yada.

          Do one at a time, or you will not see accurate results.

          Rick E. (aka RicardoMarine) Gresham, Oregon
          2850 Bounty Sedan Flybridge model
          Twin 280 HP 5.7's w/ Closed Cooling
          Volvo Penta DuoProp Drives
          Kohler 4 CZ Gen Set

          Please, no PMs. Ask your questions on forum.


            Rick, thanks for the ideas. I should've thought of the swapping of parts. You're right that vacation is not the time since the motors seem to be running fine (albeit with some extra gas) and we do want to continue the vacation. Thanks again.