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OMC 5.0 305 wot lag and power surge

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  • OMC 5.0 305 wot lag and power surge

    Having an issue with my 5.0 305 OMC in my 1988 215 four winns sundowner. When i slowly give it throttle I can get it close to Wot but once I give it full throttle it looses power and speed. If I leave it at 3/4 throttle sometimes itll surge forward with more power then lose power and it keeps going back and forth like that. It has been getting a bit worse and now I can never really get it to wot no matter how slow I give it more throttle. It seems like a carb issue because of the random power surges and how it runs fine until 3/4 throttle. It is worse after running the boat for awhile, doesnt do it as bad when cold. The boat has had the points replaced with a pertonix kit and has had a carb rebuild within the past few years. It hasnt been run for two years but I have burned a full tank through it now and have ran seafoam in it as well. I am suspicious that maybe the secondaries arent opening up like they should but really lost as to where to start to try to get this solves. Thanks in advance.

  • #2
    Welcome aboard: how 'bout the basics? Fuel filter, spark plugs, compression?
    [ATTACH=CONFIG]temp_270443_1499813187632_202[/ATTACH]

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    • #3
      Start by checking the filter at the fuel inlet on the carburetor. You will need a 1" open end and either a 1/2" or a 5/8" flare nut wrench to keep from damaging the fitting. Then drain the contents of the large filter on the engine into a bucket to see if there is any water present. That may be all that is the problem. Inspect the hose from the tank to the fuel pump to be sure it has not collapsed internally. Some fuel tanks have a small filter inside of the suction tube that can get restricted.
      1980 Donzi 18'. 2+3 6.2 MPI Alpha 1

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      • #4
        Originally posted by southkogs View Post
        Welcome aboard: how 'bout the basics? Fuel filter, spark plugs, compression?
        Sparks plug were replaced not too long ago, compression is good. My grandfather owned the boat about 4 years ago and he put the electronic ignition new plug wires in and a carb kit when he had it. He sold it to a guy who used it maybe twice and then I bought it back. I haven't checked fuel filter is there more than one to check? I know there's the screw on one which I'm assuming I can get a new one at any parts store but is there an inline one as well?

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        • #5
          and a carb kit when he had it.
          Ayuh,... A carb is rebuilt only until more crap is pumped into it,...

          I'm guessin' ya got a spin-on canister type filter, 'n probably another in the carb's inlet fittin', as mentioned above,...

          As for the spin-on filter, some parts stores might carry 'em, but it's an OMC part, the threads are different than the Merc equivalent,...
          The filter screen in the carb's inlet is more likely to be found in an auto parts store, as rochesters used 'em for years,...
          Just be forewarned, there are different lengths,....

          When ya pull the canister filter, pour it into a clear container to Inspect it's contents,....

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          • #6
            Originally posted by Bondo View Post

            Ayuh,... A carb is rebuilt only until more crap is pumped into it,...

            I'm guessin' ya got a spin-on canister type filter, 'n probably another in the carb's inlet fittin', as mentioned above,...

            As for the spin-on filter, some parts stores might carry 'em, but it's an OMC part, the threads are different than the Merc equivalent,...
            The filter screen in the carb's inlet is more likely to be found in an auto parts store, as rochesters used 'em for years,...
            Just be forewarned, there are different lengths,....

            When ya pull the canister filter, pour it into a clear container to Inspect it's contents,....
            I pulled the spin on filter and drained it into a jug. Had a lot of particulates in it and the gas was green which I thought was odd. Didn't seem like it had water in it but the filter definetly was full of junk. Haven't had a chance to pull the carb one yet.

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            • #7
              but the filter definetly was full of junk.
              Ayuh,.... There's probably more of the same in the tank,....

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              • #8
                Originally posted by Bondo View Post

                Ayuh,.... There's probably more of the same in the tank,....
                Any thought as to why the gas would be green? The guy who my grandpa sold it to said he ran like 100 octane fuel in it or something would that be dyed green? Going to change both filters as well hopefully that'll solve the issue. But I have ran probably close to 40 gal of new gas through it already so I don't think the condition of the fuel itself would be a factor at this point

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                • #9
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                  Av gas is colored as well as racing gas, some fuel additives will also change the color if you put enough in it. 100 octane is actually "over octaining" the fuel. The compression ratio on this engine does not need it and it will perform better with 91-93 non ethanol.
                  1980 Donzi 18'. 2+3 6.2 MPI Alpha 1

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