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1988 175 hp Yamaha lose of top end power

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  • 1988 175 hp Yamaha lose of top end power

    Not sure what is going on. Rebuilt carbs, new filters & plugs recently.
    Boat took a crap 2 weeks ago and put 2 fuel pumps on it and it ran great for several hours of use. Then head out into the ocean and a little bump from a swell and it is like it lost power when there is a load. I cannot climb a wave but it will run at 3900 rpms using 12 gallons per hour in decent water. It normally runs at 9 gallons per hour at that rpm. As I tried to get back home I would give a little gas and it seemed like the engine would intermittently try to take off then bog down like it cannot get enough spark or fuel. Something is killing its rpms. It is idleing fine but you can tell it is a little off. Any suggestions? Starting to think it might be some sort of sensor that is not working.

  • #2
    sounds to me like carbs got clogged again, are you using a new separator, clean gas ?

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    • #3
      Replaced all filters and seperator 2 months ago. Just refueled boat because I a have been running the boat regularly. It has not been sitting.

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      • #4
        You might check compression, check for spark and look at spark plugs.
        Regards
        Boats.net
        Yamaha Outboard Parts

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        • #5
          Replaced spark plugs with set I had removed earlier w/ 16 hrs use. Sounded better at idle just need to take it for a spin. I will check compression if it does not run right on the next use. It is getting spark on all cylinders from what I can see with the spark tester. I Plan to also bring a gas can to plug into the engine to verify it is not fuel tank or seperator.

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          • #6
            try running at night on hose and look for errant spark around coils,even take off the rear cover to expose coil leads.
            if it still bogs under load, feather choke and see if that helps.

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            • #7
              Thank You, Good suggestions. I will give it a try tommorrow night.

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              • #8
                Did compression check & found 125 to 115 lbs on all cylinders. Started engine in the evening and no sparks noted from the coil/plug area. I will give it a run in the next few days and see if she is running ok from replaced spark plugs. I have a feeling it will be fine because it is idleing better than before the plug change. But when will it do it again and why is the question. Keep you updated.

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                • #9
                  carbs recleaned.

                  I had similar problem, on mine. Ended up cleaning the carbs again! end of problems. It only took me about 1.5 hours to do. used same gasket's (assumin your's were currently replaced). and Air compressor. I did find 2 carbs clogged.

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                  • #10
                    Finally took the boat out yesterday after thinking the boat was fixed. Boat runs great at idle but at top end it is now surging ex: 4100 to 4000 rpm continually. Almost like the sparkplugs coil are kicking in and out as loss of power. I am thinking it may be a spark plug wire or coil not making a good contact. I used a tester and found that it glows lightly on each cylinder but not sure if it really gives a good enough reading. Thinking of buying a couple of coils and trying them on each cylinder. Any suggestions would be appreciated.

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                    • #11
                      sounds like you still have a clogged carb or 2

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                      • #12
                        Took the boat out again yesterday since I wrote this and it ran perfect for a 12 mile run.
                        Now I am confused. It did not skip a beat and had the normal power.

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                        • #13
                          If its a surge thats a sure sign of running out of fuel. Sounds like you have ample fuel for the idle demand but not enough as revs increase.

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                          • #14
                            Just an update. Rich of JUST-In-Time gave me a suggestion to look for an air leak in the fuel lines. I added tie wraps on the fuel lines which improved it but the boat did start surging after running good, then corrected itself later. I have used the boat three times since the surging and it runs like clockwork now. Not sure what the problem really was but it idles and runs great now.
                            Thanks Rich, you are pretty sharp when it comes to Yamaha's.
                            Last edited by wildturkey; 02-01-2010, 01:48 PM.

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                            • #15
                              glad to hear it's good now, yamis are great motors.

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