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Yamaha 8hp 4 stroke kicker

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  • Yamaha 8hp 4 stroke kicker

    My son left his 8hp Yamaha electric start connected to a battery. Start button is on tiller. In a heavy rainstorm his battery box filled with water and shorted the terminals. His roommate texted him his motor was making a horrible noise and disconnected it from the battery and the noise stopped. Now I have the motor and trying to ascertain the damage. I see the oil pressure light is red when turning it over (should be green). There is spark and compression however it appears to be low 145 lbs. It does not start or even backfire. Would appreciate any suggestions to aid in repair?

  • #2
    An update. I rechecked the compression and with throttle wide open I got readings of 195lbs on both cylinders so compression is not an issue. I have a working 8hp yamaha non electric start and got readings of 180 on both cylinders. I have spark, compression and fuel, what am I missing. The oil pressure light red is normal and presumably changes color when the engine starts. The kill switch functions as I have a strong spark. Is there another fuse other than the 10 amp I have located and tested good?
    Last edited by rivermanone; October 12th, 2019, 02:53 PM.

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    • #3
      How did you check for fuel? Wet spark plugs?

      Did you drain the carb / portable tank and check for water in the fuel?


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      • #4
        Kill lanyard switch would be suspect for me.

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        • #5
          No water in my son's fuel. I drained it and connected to my boat which has a water separator. I have spark so I don't suspect the lanyard kill switch. Am I wrong? I have been swapping parts from my 8hp motor which is non electric start but otherwise the same. I swapped plugs, cdi, coil, and his parts worked in my motor, but my parts don't help his. I have his voltage regulator/rectifier removed and will try on my motor tomorrow. I don't know what's left. Are there any parts left in the ignition system other than the stator?

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          • #6


            If you have spark, AT THE PLUG, when cranking, the ignition system should be fine. Short of the timing being way out..

            Agreed, if the lanyard was pulled/an issue, it wouldn't have ANY spark..

            You didn't answer, are the spark plugs getting wet with fuel?


            Something to look for, possible flooding. Should a carb dump fuel into the crankcase, it'd foul the spark plugs and not fire..

            Might also try spritzing some pre-mix down the carbs when cranking to see if it is a fuel delivery (lack of) issue..

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            • #7
              yes, plugs are wet with fuel. I have not even got it to fire once. It turns over fine. I removed his plugs and put them in my motor and they worked. I put mine in his and nothing. My thought is the spark jumps to the block when the starter turns over but maybe when everything is connected plug wires to plugs something grounds everything out. I am guessing that the problem lies under the flywheel that I have been unable to remove. I'm thinking it goes to the dealer. I have tested everything I could access by removing the parts and confirming they work in my similar motor.

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              • #8
                didyou check timing . if timing marks on cam shaft wheel and flywheel is lined up?

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                • #9
                  A motor needs good compression, good spark at the proper time, and the proper fuel to air mix to fire up and run.
                  you say you have good compression and spark,

                  so you are left with is it sparking at the correct time, and the proper fuel to air mixture if the fuel is good.

                  timing can be checked with a timing light.
                  too much fuel in a carb motor can be checked some what buy pinching off the fuel line to the carb to starve it of fuel .

                  too little can be checked by spraying fuel into the carbs or some starting fluid

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                  • #10
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                    Update: There was a garden growing in the carb. Carb removed and cleaned properly now the motor runs properly. Thanks for your help.

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