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Engine issue/prop?

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  • Engine issue/prop?

    Hi everyone I recently bought myself a 17ft glasply. with a Johnson 90hp. I installed a tach and am only turning 3200rpm. I cant seem to find the issue. I have installed all new fuel lines, water separator, anti syphon valve, new plugs,checked high speed and they were not clogged. engine runs good just no performance. oh and compression on engine was very good. the prop size is a 13 1/4 x 17. any ideas. im new to the boating world. this is my first fishing boat.

  • #2
    One thing to check when not running is to move your control to full throttle then look to see if you are getting full open at the carb/carbs.

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    • #3
      thank you

      Originally posted by 18ftTrophy View Post
      One thing to check when not running is to move your control to full throttle then look to see if you are getting full open at the carb/carbs.
      Thank you for the reply. Yes I have checked that as well. all is good there

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      • #4
        Propeller May be pitched too high. What is max operating RPM for your motor? Probably one of the Forum members has a similar set up and can give you some advice.
        The cruise liner QE2 moves only six inches for each gallon of diesel fuel that it burns.

        1982 28' Long Cabin "Molly Brown" sweating through a long hot summer. Massive California forest fires fill our sky with smoke. SUP paddlers and kayakers transit the harbor with abandon, thinking they have the right of way over all boats.

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        • #5
          Welcome aboard, One2....

          Hopefully someone from the Glasply brain bank will chime in with some ideas for you soon!
          -- Tim Taylor

          1979 Glasply 21-foot I/O Overnighter w/ 5.0L Volvo-Penta duoprop (Cardinal)
          1982 Glasply 16-foot runabout w/ 50hp Mercury OB (JV Junior)
          1978 Glasply 19-1/2 foot runabout, project boat (Beer Goggles)


          I didn't say it was your fault, I said I was blaming you.

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          • #6
            Book says 4500-5500

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            • #7
              13-1/4 x 17 doesn’t sound overly aggressive for the prop. Too much pitch would have been my first guess too, but it’s just 17....
              -- Tim Taylor

              1979 Glasply 21-foot I/O Overnighter w/ 5.0L Volvo-Penta duoprop (Cardinal)
              1982 Glasply 16-foot runabout w/ 50hp Mercury OB (JV Junior)
              1978 Glasply 19-1/2 foot runabout, project boat (Beer Goggles)


              I didn't say it was your fault, I said I was blaming you.

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              • #8
                One2many
                More thoughts while we wait for some experts to sign in:
                Transom height - the splash plate on the lower unit should be even or slightly above the bottom of the boat.
                Boat bottom clean?
                Boat weight, is water trapped under the floor?
                Weight distribution when you are on plane? Does the boat run fairly level at speed?
                Assuming the tach is accurate, see if you can borrow a propeller or two to do some testing.
                Keep us posted.
                The cruise liner QE2 moves only six inches for each gallon of diesel fuel that it burns.

                1982 28' Long Cabin "Molly Brown" sweating through a long hot summer. Massive California forest fires fill our sky with smoke. SUP paddlers and kayakers transit the harbor with abandon, thinking they have the right of way over all boats.

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                • #9
                  A 17 pitch blade wouldn't cause a drop of 1500-2000 rpm from WOT range. If the boat is planning normal I can only think of one thing. I know you said it has new plugs so did you make sure they all have good spark? it sounds like its down a cylinder or the CPU module has gone to crap. All guesses without more info. If you haven't all ready pull the plugs and check the spark.

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                  • #10
                    is the tack set correctly for the number of poles on the stater,there is a switch on the back? what speed are you going?
                    1980 2400 Cuddy I/O, 2017 Cummins 4BT coupled to a Volvo DP-SM with F9 Props, and a 2014 Mercury 15HP Pro-Kicker "LOOSE CHANGE"

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                    • #11
                      I'm pretty sure I set the tach right. I'm only getting 22mph out of it. As far as getting it on a plane that's part of the problem. I understand I'm running a little heavy due to the 15hp kicker I have on it. But it's my understanding it weighs the same as the 9.9 I wanted. The lack of power makes it feel like a slug.

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                      • #12
                        Tell me more about this CPU. It's a older 85 90hp Johnson I believe the year us

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                        • #13
                          One more thing. I was going to try a bigger prop just to see what it would do. Maybe get it out of the hole better idk. Well as I grabbed more throttle what felt like it popped out of gear. Would not go in forward or reverse after that. Needless to say now the lower unit is off getting looked at. So more problems now. I'll keep everyone posted. Thanks for all your imput

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                          • #14
                            Originally posted by One2Many View Post
                            Tell me more about this CPU. It's a older 85 90hp Johnson I believe the year us
                            Older engines don't have the computers running them like the new ones but if the module for the electronic ignition is bad it could be the problem. That prop on a 17' GP should be fine at 90hp. Do you have working trim? Still sounds like lack of power from the engine. Did you check for spark on the plugs? One could be bad. Crazier things have happened with new plugs.

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                            • #15
                              Yes it has hydraulic trim. I will do a spark test and get back with results

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