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2000 70HP won't go over 2-3000 rpm

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  • 2000 70HP won't go over 2-3000 rpm

    Hi, I'm new here and hoping I'm posting this in the correct thread. I have a 2000 70hp johnson two stroke that's been acting up a bit. The motor was serviced about 2 years ago, when the carburetors were cleaned out, seals replaced, that kind of thing. Most of the time, it runs fine, around 5500 rpm, when the engine is fully open. For a few years, but only very occasionally, the engine will be running smoothly, and then 'cough', and then not get above maybe 2000rpm and a much lower speed. Not fully stall, just not getting above the middle of the engine's ability. Shutting the engine off and letting it sit a minute fixed the issue, and the motor ran as it is supposed to once I restarted it. I never gave it a ton of thought, since it wasn't a persistent issue. It was quirky, but ultimately didn't impact my time on the water.

    It has been happening more frequently recently, and a couple times now, restarting the motor hasn't fixed the issue - it just caps out around 2000rpm and sounds audibly different than when it is running correctly. Letting the motor sit for a lot longer fixes the issue (i.e. starting it cold, the engine runs normally). Here is a 5 second youtube clip of the motor when it's not running correctly (this with the throttle lever nearly fully forward) - here's a different time, when the rpms were closer to 3000 at fully open. I didn't take a video of what it sounds like normally.

    When it's running like this, with lower maximum rpms, the engine shakes more than normal when it's running. Are there some simple steps I can take to trouble shoot this before going to a marina to get it looked at? Filters to look at, connections to check, that kind of thing? Do you know what would cause something like this? Thank you for your help (and I'd be happy to give any other videos/pictures/etc if you need them or answer questions).

  • #2
    not running on all cylinders need to clean carbs replace plugs and check fuel pump out put. to do that take off main feed line from pump to carb put in a class container and turn motor over if pump is good it should spray fuel continually if it's bad it will pump good at first then start to die off.

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    • #3
      If pumping primer bulb when acts up makes a difference then I might suspect fuel issues. But you say not firing on all cylinders, that makes me think electrical, unless RPMs are going into safe mode/ limp mode? That might indicate a sensor acting up, or blockage in cooling passages causing sensor to protect motor, limiting RPMs. Or, maybe timing coils, plug coils, plug wires acting up.

      Good luck.

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      • #4
        i have run in to problems when the primer is hard and u can't pump it and it is a bad pump i'd suspect that it is a bad plug or a fuel issue start with the easy stuff first put new plugs in and see what happens.

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        • #5
          You might also check the neutral switch & shift sensor. If starting to act up (intermittently) one could cause these same symptoms. The neutral switch usually prevents cranking, where the shift sensor prevents motor from going above 3k RPMs (if intermittent, it will act fine sometimes, other times it's stuck in neutral), limiting RPMs.

          Good luck. Post back if you find anything.

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