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96 Johnson 50hp dies minutes after running WOT

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  • 96 Johnson 50hp dies minutes after running WOT

    Motor is on 20' pontoon boat and had motor rebuilt less then 1 month ago. I've had it out once and runs fine at 1/2 throttle and less, but running WOT for any amount of time and motor dies. Needless to say it's been sitting with the mechanic for the last week, but he seems to be at a loss as to why. He says he can get it to start and run, but the next time it will be hard to start so he thinks it is electrical, but so far everything tested fine for him. Brief overview - lost lower cylinder - new sleeve, piston, rings, etc. installed. Now this. Anyone have any ideas?Thanks in advance.Bill


  • #2
    Re: 96 Johnson 50hp dies minutes after running WOT

    I guess its the power pack. If not maybe fuel flow problems. Good Luck!!

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    • #3
      Re: 96 Johnson 50hp dies minutes after running WOT

      Hard to say Bill without some info to go on, like compression on the cylinders. Even though the one sleeve was replaced, do we know for sure if the exhaust and intake ports edges were broken to prevent catching a ring?Any overheat warnings or do you know for sure it was not over heating?May be heat related....once a particular component gets hot, it's kicking out....maybe power pack or power coil.Have you tried squeezing the primer bulb when she slows down to see if it speeds back up? When the engine was rebuilt, were the carbs overhauled also? This is practically a must.Just need answers to help with the question.
      When in doubt...use the manual

      Rayland, Ohio....Along the Muddy Banks of the Mighty Ohio River.

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      • #4
        Re: 96 Johnson 50hp dies minutes after running WOT

        Jim,Cylinder compression is 120 in each. No overheating alarms or lights go off. The carbs have at least been cleaned and new gaskets installed. I can't guarantee that the mechanic has "rebuilt" them even though he leads me to believe that he has. I thought it might be starving for fuel but when I did have it on the lake last weekend I had a friend feel the bulb on the gas line when it started dying (it was hard) and even try to pump more gas which didn't help. Overheating is what I think it's doing as the water that is coming out is warmer than I would think it would be. I've only owned the boat about 6 weeks so I have no history with it. The thermostat has been replaced as well.Hope this helps.Bill

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        • #5
          Re: 96 Johnson 50hp dies minutes after running WOT

          Hi Bill, I'll try to give some suggestions to help based on your last post.I would still try the spray bottle when it starts to die. I base this on what you said about the primer bulb being "hard". The buld should soften after running a while. It will pump up initially and be hard because the engine is not using the fuel. But after starting and running, it should soften up as the engine uses fuel.The hair dryer method may also tell you something although it sounds more fuel related than ignition. As the engine is running, take a hair dryer and blow the hot air onto the ignition components one at a time. The power pack is a good place to start. If the engine dies, then that may be your bad boy. Blow the air up under the flywheel to heat up the coils also.If all the above fails, and I'm going to assume the engine is equipped with VRO, check the pulse limiter to the VRO motor end. It will be a fitting between the block and VRO pump. This regulates the vacuum and press. to the pump from the block. This may have a partial pluggage in it and not allow the VRO pump to serve enough fuel to the engine at WOT.Give it a shot. And watch for other ideas from other members of the forum.Good Luck and keep us posted.
          When in doubt...use the manual

          Rayland, Ohio....Along the Muddy Banks of the Mighty Ohio River.

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