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02 Merc 125hp 2 stroke prop pitch questions

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  • 02 Merc 125hp 2 stroke prop pitch questions

    I have a 19' aluminum dual console boat with a 02 Merc 125 2 stroke on it. The recommended max rpm is 5250 for the motor, I can definitely get a ways past that with my current prop. It's a 3 blade 19 pitch. It's running about 35-37 mph on flat water @5,000. Could probably get 6,000 out of it if I pegged the throttle... Would a 4 blade 21 be to much of a jump? Same diameter,which I think is 13 I believe.

  • #2
    No. Might try a 23P 3 blade too.

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    • #3
      Originally posted by Vernon351 View Post
      I have a 19' aluminum dual console boat with a 02 Merc 125 2 stroke on it. The recommended max rpm is 5250 for the motor, I can definitely get a ways past that with my current prop. It's a 3 blade 19 pitch. It's running about 35-37 mph on flat water @5,000. Could probably get 6,000 out of it if I pegged the throttle... Would a 4 blade 21 be to much of a jump? Same diameter,which I think is 13 I believe.
      Don't hold your breath on going over 5250 regardless of what prop you are running....unless somebody has removed it....and apparently they have: That engine (like my 115 of the same year) is a 2+2 and has a 5250 RPM rev limiter module...port side, midway fore-aft, just above lower cowling where hood seats. They have that engine choked down for some reason.....Faztbullet knows why. He did say piston skirt malfunction problems on some engines over revving but I don't know the reason on the 2+2, especially since it's so low....he will probably pick up on this and provide his reasoning.
      If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

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      • #4
        I did not realize it had a rev limiter, thanks. That kind of makes me question weather my tach is working properly or the limiter is working properly. Because the first time I took it out I hit 5300-5400 rpm and had a little throttle left. I backed off at that point obviously. If the limiter was bad would it allow over rev?

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        • #5
          Either way, I can hit rpm limit with the current prop. I'm not looking for any more speed really, rough water handling and lower rpm control and whole shot are more what I'm concerned with. So would a a 4 blade 21 pitch fit the bill? Or does anyone else have a better suggestion?

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          • #6
            What's the current pitch installed now, is it a 3 blade prop ?

            Happy Boating


            Sea Rider 320, 380 Sibs, 450 Rib, 2 Strokes Tohatsu 5,18 & 30 HP Proud Smokers

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            • #7
              I just bought this boat last year and spent some money on props before I found the real problem...a clogged fuel filter. I was down playing around with 17P props when it currently hits the limiter in cooler weather with a SS Laser II 20P. The limiter works on mine.

              When you can go to go-fast.com prop slip calculator, a trusted reference for many years, and come up with negative slip you know something isn't telling you the truth....or the rev. limiter has kicked in and modified your answer.

              On good hole shot and good top end I like ported props. Get the best of both worlds. They are getting real popular so there must be something to it besides the success I have had with them since 1989.
              If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

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              • #8
                Only some of those motors had rev limiters and they are primarily jets. The problem with going over 5250 is breaking the piston skirts. There is a service bulletin for that exact issue ,not to mention that motor falls off its powerband pretty quick. Are you sure your tach is.correct my 125 on a 17' fiberglass bowrider with a 19" pitch maxed out at 5250 rpm.

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                • #9
                  Current pitch is a 3 blade 19" pitch. I'm not 100% sure the tach is dead accurate, but I've been around motors long enough to tell it's definitely up there in the rpm. It my be a couple hundred off at best, I will change the tach soon. But either way I had more throttle left to go. So pretty much guarantee I could over rev with current prop.

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                  • #10
                    I’d be after a good 3 blade stainless 20/22” laser 2

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                    • #11
                      Originally posted by QBhoy View Post
                      I’d be after a good 3 blade stainless 20/22” laser 2
                      I lucked out on getting my 20P. I had a nice, shiny, Ballistic 24XL that I ran on my 90 and was the engine used in my avatar. Since I sold the rig (but kept that prop...boat had another Ballistic when sold) and bought a 115, at 2:1 vs 2.3:1 for the 90, 24P, especially with it being a large blade area XL, it was way too much for the current boat.

                      Went into a local dealer one day and shopped his used props. Found what I wanted and plopped the Ballistic on the counter. I said let's trade....he said ok. That was that.
                      If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

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                      • #12
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                        Originally posted by flyingscott View Post
                        Only some of those motors had rev limiters and they are primarily jets. The problem with going over 5250 is breaking the piston skirts. There is a service bulletin for that exact issue ,not to mention that motor falls off its powerband pretty quick. Are you sure your tach is.correct my 125 on a 17' fiberglass bowrider with a 19" pitch maxed out at 5250 rpm.
                        That's what Faztbullet said about over revving and resultant potential damage to engines. What I don't understand is why that particular engine, actually the whole series, 100-125 hp., were limited when my previous 90, same year model, was rated to 5500 and I ran it in the 57-5800 range every chance I got. Course the 90 was 120* firing and the 4 cyl is 2 stacked alternate firing twins, 90 degrees out of phase.....does 30 degrees of phase angle make that much difference?
                        If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

                        Comment

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