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89 Evinrude 88 SPL rpms?

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  • 89 Evinrude 88 SPL rpms?

    I have a 1989 Evinrude 88 spl with a 13x19 prop pushing an 18 foot sea pro center console. With just me in it and not much gear, the boat turns a maximum of 4800 rpms and 31 mph. Should I be using a different prop? Should the motor be turning in a higher rpm range.I have fresh plugs in it and 87 octane. Any help would be appreciated. The motor is mounted in the lowest slot on the transom if that helps, and it has power t/t.Thanks,Jon


  • #2
    Re: 89 Evinrude 88 SPL rpms?

    You're 1000 rpm too low. Raise the motor to get more WOT rpm's. Change the prop as required. What brand/style prop are you using now?Good luck!

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    • #3
      Re: 89 Evinrude 88 SPL rpms?

      I got it cheap $130 at West Marine.It is a Michigan Wheel, I believe. The blades appear to be cupped.How high should I raise the motor? I am new to all of this. You suggested changing the prop as required. Which way should I go?I tried a 13.75x15 for a little whie. The boat revved to 5800, but I lost top speed considerably. I feel that the boat should be travelling at 35 mph or better. Am I expecting too much?Any more help you can give will be greatly appreciated!Jon

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      • #4
        Re: 89 Evinrude 88 SPL rpms?

        slapshotjh, My 2 cents worth, I think, from past experience, a 17" pitch would put you in the 55-5600 RPM range (good place to be) and if you don't mind a little sweat, the trial & error method for optimum height adjustment is worth the trouble. The highest adjustment on transom possible without cavitating in turns. Keep tring til you get that 35 mph, it's possible...

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        • #5
          Re: 89 Evinrude 88 SPL rpms?

          I had some time to work on it this evening, I raised the motor one notch up from where it was at the bottom.I was fooling around looking at the throttle positions in relationship to the linkages on the carbs to open the butterfly valves. I can push the butterfly valves open further with my thumb after the throttle has reached WOT on the console. Do I need to adjust this so that the butterfly valves are fully open (I am assuming they open 90 degrees?)Will test the revised motor height tomorrow. Will get another prop this weekend.Jon

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          • #6
            Re: 89 Evinrude 88 SPL rpms?

            You are very close to insuring W.O.T. Remote fully open and butterflies fully open. At this point the throttle stop screw must be set to prevent the butterflies from opening further than perfect horizonal. Operate the remote a few times and reset as needed. Now would be a good time to check advanced timing (ball park).

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            • #7
              Re: 89 Evinrude 88 SPL rpms?

              I will adjust the throttle stop as needed. How do I check advanced timing? I do have a timing light that I have used for automotive purposes.

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              • #8
                Re: 89 Evinrude 88 SPL rpms?

                Well, raising the motor one notch gained 2-3 mph. However, top rpm still seems to be 4600 rpm. Will jumping down from 13x19 to 13x17 prop raise my rpms and give me more speed? How about that timing?

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                • #9
                  Re: 89 Evinrude 88 SPL rpms?

                  You must first find top dead center (TDC) for #1 cyl. Notice the timing pointer above top carb. pointing at flywheel teeth. It is adjustable and should point to TDC when you have confirmed the #1 piston is at TDC. With timing light to #1 cyl. you are ready to proceed with initial/pick up timing (idle speed). This setting is not as critical as max. advanced timing. Next comes advanced setting. Look under flywheel and notice the timer base rotating with the throttle to a certain point. The point at which this timer base stops will determine your fully advanced timing. It is adjustable. You can check setting two ways. First, (ball park) remove plugs & ground plug wires, fully open throttle or at least until timer base is fully rotated, then turn key switch on and jump solinoid to spin eng. Timing light will show actual setting (BTDC) before top dead center. Set timer base stop to desired specs.Usually listed on air silencer. This setting is usually +/- 2*. The better way is in the water and running to full timer base rotation...WOW I sure hope this goes through 'cause I sure can't write all this again. Good night...

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                  • #10
                    Re: 89 Evinrude 88 SPL rpms?

                    About the prop, I don't know if the 17" would be worth spending the money, but if you had access to a loaner I would certainly give it a try. 35 MPH or bust! Good night #2

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                    • #11
                      Re: 89 Evinrude 88 SPL rpms?

                      What you've done so far is good. I think you really need to try that 17" prop. It should bring you to optimum rpm (about 5000-5500rpm)and top speed at WOT of around 35mph.Red sky at night. . . . JB
                      sigpic

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                      • #12
                        Re: 89 Evinrude 88 SPL rpms?

                        Slap, this would be a good time to consider a OMC SST stainless propeller. The SST is a cheaper alternative to a polished prop. (they are generally painted black) The older ones were telflon coated and I think the newer ones are powder coated. There are many of these props on E-bay. Type: OMC Propeller in the search window. If you buy a used one, just make sure that it is in perfect condition (no nicks or dings) and preferably has never been repaired. You should expect better overall performance and the ability to raise the engine even higher. How high is the cavitation plate above the bottom of the boat now? Does the engine mount right on the transom, and is the transon stepped out from the trailing edge of the boat bottom? Does the motor have power trim? If so how are you using it at top speed? In general, the further away the motor is from the trailing edge of the boat, the higher you can raise the motor, stainless props in general are more condusive to this.You dont want to get carried away here as you can starve the engine for water. From what I have heard it seems like you could go one higher, if the aluminum prop begins to cavitate, the stainless at the same height probably will not. Its important to get the motor set at the proper height before you make a final determination of the correct prop, and every prop runs differently especially when you switch to stainless. A 19 pitch stainless may run 200-300 rpm higher than the aluminum, also expect to lose maybe 200 rpm with passengers. Is there a prop dealer around that will let you experiment? Just some food for thought, it seems that you are on the right path with great previous advice. If you go no further with your experiments, then a 17 pitch aluminum of the same style seems right to me.

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                        • #13
                          Re: 89 Evinrude 88 SPL rpms?

                          In Ebay search type: OMC prop*

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