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New Nissan 20 hp knocking at wot

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  • New Nissan 20 hp knocking at wot

    Hey guys, looking for some advice. Have 3hrs or so on a new Nissan 20hp. Last trip out at wot the engine starting making a knocking sound, as soon as I let up a bit it would stop. Only happened at wot. Checked to make sure nothing was banging around. The previous trip I had two other guys andno noise at wot. This trip I was by myself, is this noise the esg kicking in due to high rpms? Gas is fairly new, 2 weeks old. Oil level is fine. I have a 1654 grizzly, motor runs great otherwise. Trying to decide if I need to take it to the dealer or if I need a bigger prop?


  • #2
    Re: New Nissan 20 hp knocking at wot

    Also, broke in according to Nissan. Just realized I forget to vent the tank, will head out tomorrow with tank properly vented and a higher octane gas to see if that was the issue.

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    • #3
      Re: New Nissan 20 hp knocking at wot

      If the ESG kicks in, the spark will stagger, which will sound like a weird misfire. What is your WOT RPM?
      Paul
      Certified TLDI Technician
      Buffalo NY USA

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      • #4
        Re: New Nissan 20 hp knocking at wot

        I don't have a tach in it, not sure of the rpms. Sounds like I will need to get the rpm level when its happening to know for sure.

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        • #5
          Re: New Nissan 20 hp knocking at wot

          If you can borrow a good shop tach for testing, cool. If you prefer to install one permanently in the boat, they are available (from any dealer, including me) with a black face, Part# 3AC726400M, $77.96 or white face Part# 3AD726400M, $77.96. If you get the Factory tach, spring for the 361725390M LEAD WIRE TACH 20', $46.62 (for tiller models), or 3R0725371M LEAD WIRE, METER $58.94 (for remote motors), or you can make up your own harness.
          Paul
          Certified TLDI Technician
          Buffalo NY USA

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          • #6
            Re: New Nissan 20 hp knocking at wot

            What you described sounds exactly like the rev-limiter kicking in. It didn't make noise with two others (extra weight) but by yourself it was. My 2009 Tohatsu 20 4-stroke did this exactly, and still does.

            I am running it on a 1436 Alweld and upped the prop to 11" which was the longest pitched prop I could find. Not to hijack, but are there any longer pitched props out there for this motor?

            I still don't ever run it at WOT, and IMO (from what I've read) running it at WOT all the time and pushing the rev-limiter will make your motor more prone to failure at some point. I would rather lose 2-3mph over a few hundred RPMs than have something explode on my engine.

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            • #7
              Re: New Nissan 20 hp knocking at wot

              Had the boat out today with another person and no noise at wot. Fairly certain it was the esg kicking in. When I'm running by myself I just won't run wot, usually not by myself anyway or I have the dog/decoys etc. Thanks for the advice, I'm relieved it wasn't an issue with the motor and I know what caused it.

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              • #8
                Re: New Nissan 20 hp knocking at wot

                Go for an induction tach, check at which wot rpm the ESG kiks in, place a prop pitch that will rev near max ESG but without kiking in with you alone, that way will boat smooth at wot if you like speeding sometimes.

                Happy Boating
                Sea Rider 430 > 450 Rib Tohatsu 18L > 50 HP Proud Smokers

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                • #9
                  Re: New Nissan 20 hp knocking at wot

                  Sounds to me like the rev limiter was kicking in. I run a 20hp Tohatsu which is same motor different cowling and stickers and I recently have verified that my rev limiter is kicking in. You will need a tach to know for sure though. That's what I had to do. Mine was making the knocking sound under light loads exactly as you said yours is. I'm running it on a 1442 fatbottom now and it still does it. I'm about to switch to 11 picth as soon as I get the extra $. I'm suprised that the 16 foot grizzly is allowing the motor to rev that high though. Grizzlys are heavy hulls for their size. But the basic just of this is what you've described sounds exactly like what I had to confirm. The Tohatsu prop chart wasn't much help iether cause there's a lot of factors it doesn't take into consideration that you will only have to try to find out. Good luck
                  My mind is on the river 24/7. Too bad my body has to go to work.

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