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mercury bottom carb blowing out

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  • mercury bottom carb blowing out

    1995 40hp 4cyl mercury running rough bottom carb is blowing out while motor is running I can cover carb with my hand and makes no difference in running. would it be compression blowing out? any suggestion or idea greatly appreciated. thanks

  • #2
    Now that sounds like a stuck/broken reed valve(s).

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    • #3
      ^^+1 Also my thoughts.
      '96 Larson 174 SEI BR. 4.3LX 4 bbl Weber s/n 0F786604. Alpha One Gen II s/n 0F709315

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      • #4
        could the reeds be behind the carbs? Or hard to get to?

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        • #5
          On a 4 cylinder they are internal on the crankshaft I believe.-------Your serial # is ?-----Not easy for a novice.to fix-------But there are other checks to do first !!!------Compression first.----Then check for spark on each lead and see if it jumps a 3/8" gap.-------Sounds like the bottom carb is flooding.--------The reeds are very reliable but could be held open by seagull feathers I suppose.

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          • #6
            serial # og140424 model #40elpto thanks

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            • #7
              If compression is good pull the carb bowls and clean them out, clean the floats. I had the same issue and it was a chuck of junk in the bowl.

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              • #8
                This motor is driving me crazy. Bottom carb blowing out. I can cover completely makes no difference .I have tried all suggestions except reed valves, and now I find that the fuel pump is not working. I replace the pump, still not working. So could the pump not pumping be a symptom of reed valves. Thank you guys for your tips and ideas I am at wits end

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                • #9
                  I believe in inspection / trouble shooting.-----Did you take the old pump apart or did you just run out and spend $ and find that motor still does not work.----Sounds like you now have a good spare pump.-------With a bad reed valve you would not get crankcase compression, thus no pressure pulse to drive the pump.

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                  • #10
                    So reed valves should be the problem? thanks

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                    • #11
                      Did you replace the check valves in the pump as well?

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                      • #12
                        I got a new pump, and had the old one inspected by a mechanic, the old pump was good too

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                        • #13
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