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  1. #1
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    Please help with my setup. 16ft superboat with 12 JP w/120 Johnson. Only 40mph?

    Had the boat 10 years now but recently changed the motor. Previous motor was a 1.6ltr 110 v4 vro Johnson with raker prop. Boat did 50mph exactly as a center console then I converted to dual console(maybe added at the most 100lbs) swapped the old 1.6 for a 2.0 v4 Johnson 120hp from early nineties. Was expecting in the high 50s low 60s but instead topped out at 41. Motor has good compression and is in great mechanical condition.

    Any ideas why a small motor with less displacement was able to push the boat 10mph faster than the newer 120?

    is it running on all cylinders?
    is the extra weight the issue?
    is the shaft longer? Should I raise the motor?

    the boat has a 12 manually adjustable jack plate.

    aslo from what I researched the newer motor is 65lbs heavier. With the same raker prop that was on the older motor Im only turning 5000k. With another mid range prop I had lying around the boat pushes 6200 rpm and does 39mph almost the same speed. Im at a loss

    experienced people please help!!!

    thanks in advance

  2. #2
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    Not that familiar, but the 1.6 was a crossflow? Compared to the 2.0 which is a looper.

    If that is the case, you just added a bunch of weight to the back of the boat. And then to boot, are you sure your new motor is running up to par?

    I went from a 100 cross that was dead on one cylinder to a 140 loop that runs like a raped ape and the difference is, tee hee hee, so much fun!!!

    Maybe you are experiencing the opposite, outside of the weight difference?

  3. #3
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    Quote Originally Posted by SS Minnow View Post
    Not that familiar, but the 1.6 was a crossflow? Compared to the 2.0 which is a looper.

    If that is the case, you just added a bunch of weight to the back of the boat. And then to boot, are you sure your new motor is running up to par?

    I went from a 100 cross that was dead on one cylinder to a 140 loop that runs like a raped ape and the difference is, tee hee hee, so much fun!!!

    Maybe you are experiencing the opposite, outside of the weight difference?
    the 110 was a cross flow with bubble back design and had roughly 100psi compression.
    the 120 has 125psi and weights 65 lbs heavier hanging directly on the rear but I may be suspect it’s only getting spark to 3 cyl.

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