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Engine Dilemma

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  • Engine Dilemma

    Hey all,

    I come to you with a unique engine situation. As it sits, my 1989 Classic 191 has it's original twin 1989 Yamaha 70 hp 2 strokes. The motors ran well last year, but were susceptible to a hick up here and there.

    In my yard I currently have an 04 Yamaha F150. The motor is sitting on my family's old Sea Ox 180. I am currently debating on whether or not to go through the trouble of swapping the twins for the single 150.

    What I am absolutely terrified of, is the boat being too heavy in the back. We always had wet feet in the Sea Ox and I hated using it because of that.

    If my math is correct a 2004 Yamaha F150 weighs 475, while twin 70's weight 446, so that an only a 29 lb difference. I can rob all the rigging off of the Sea Ox as well.

    Basically I am asking someone to check my math and tell me if it would be worth the trouble.
    1989 Classic Mako 191 - \'Tequila Rose\'

  • #2
    The math seems fine.

    If you want to see what the extra weight will feel like, fill a 5-gal

    bucket with water (8.3 lbs/gal) and ride around with it in the back.
    “On the days where I keep my gratitude higher than my expectations, I have really good days.”

    M20 project-Finally Splashed!


    • #3
      Yep - the numbers work. The difference is going to be in drive feel. the f150 will lack the torquey feel of the twin 70s, and you'll be on single engine steering as well. So it wouldn't be a bad swap. But it will be a different feel.


      • #4
        You'll probably go faster

        (+10 hp; drag from only one LU)
        NYC & L.I. - 1974 \"Classic\" Mako 20\' - Suzuki 2006 DF150 - Fly & Light Tackle, C&R[br]My boat:[br]Personal website:


        • #5
          I think youll be very pleased with that change. I would certainly do it in your position.

          I thought those old 70s were the same platform as the Yamaha 90 and weighed more like 250 each? I may well be remembering wrong, but if not, you could lose a little weight.
          Sold the 17\', moved to FL... I need a new handle.[br]1991 Jupiter 31, current project[br]2005 Everglades 243, sold[br]2012 Contender 23 Open sold[br]1989 Intrepid 246 WA--gone to Australia[br]1973 Mako 17--sold with regrets[br]1992 Mako 17--started it all[br]Pompano, FL


          • #6
            The 70hp Yamaha shared the block with the 60 (90 is a different animal) and they 70hp weight is right around 225#, so your thinking is correct. I think moving from twins to a single is the right way to go. So by your numbers it's a 6% weight difference, but I'd say probably closer to weight neutral. If there's a valid concern and your battery is not already mounted in the console, move the battery to the console and you'll be in better shape (from a weight distribution perspective) than you are now.

            Remember going to a single from twins, you are doing away with the weight from the second motor, but also the weight of - the oil in the injection tank, prop, 2nd set of batt cables, 2nd harness, controls, 2nd cables. These are NOT included in the weight specs of the 70hp motor, so your weight savings will be more than what your numbers show.

            The 70s are great motors and I just picked one up for my Whaler. If in good shape, there's no reason why you can't sell them for $1500 each. That seems to be the market value on those now and I've seen then run upwards of $2500 each. There are plenty of people looking for lightweight 2 stroke motors, especially with the cost of a new 70 running around $8K.

            Current Mqko - 1990 Mako 211 w/2006 250 E-TEC. [br]- Previous Makos 1987 20C, 1979 23\' IB, 1970s 17 Angler


            • #7
              Edit: Never mind, might actually get the motor after all.
              1989 Classic Mako 191 - \'Tequila Rose\'