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1998 90HP to a 1991 90HP Electronics Issues

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  • 1998 90HP to a 1991 90HP Electronics Issues

    A few moths ago, I purchased a boat with a 1998 C90TLRW on it. The engine needs to be rebuilt, so I purchased , what I was told was a C90TLRW engine. Used with a measured 115 psi on all cylinders. However, since I have started moving over my electronics and such, I noticed some minor differences. First red flag was the lack of vacuum attachments going to the block from the middle card. Second one was the lack of crank position sensor on the top by the engine hoist eyelet. Turns out (thanks to Crowley Marine) that the "new block" is from a 1991/1990 90HP. So far, I have noticed that the lack of crank sensor, stator, and magneto look different. Other than that, everything else bolts up fine. My question for the seasoned vets here is this: Is it possible to run the engine with my given electronics, or will I have to purchase some older types (mainly CDI and electronics under the flywheel)? I am concerned with my 1998 having electronically adjusted timing to one that needs to be adjusted manually. Any help here is appreciated.

  • #2
    sounds like you bought a used bare power head and not and engine like you mentioned.
    I do not see how you can make it work without all of the proper stuff that is needed.
    I am guessing you will need different carbs also from what you wrote


    • #3
      Yes. Its a bare power head. The carbs I have bolt up just fine, and there are only minor difference in the motor. It looks like the biggest difference are the three holes to mount the coil pulser under the flywheel. The 98 is pretty flush, where as the 91 is raised about 3/4 inch. I am wondering if I can file/cut those down to make my newer parts work. I can fabricate a crank sensor bracket as well. Wondering if I am the first person to convert an older motor to newer electronics. Luckily, it does not appear that Yamaha made any other significant changes to the block.


      • #4
        what do you plan to do about
        the lack of vacuum attachments going to the block from the middle card.

        what is wrong with your old power head that you could not rebuild it instead of trying to rig this one that is not a good replacement?
        Last edited by 99yam40; 12-09-2019, 03:35 PM.


        • #5
          The power head that I took off was used heavily in saltwater. Corrosion everywhere and had a small exhaust leak on the exhaust manifold. Turns out 9 of the bolts are seized and snapped inside of the block. The stainless bolts + salt + aluminum = a bad time. Torch and easy outs did not work, so I will eventually tap them out. Also, cylinder three has some scarring that I will eventually get to with a hone or size over. The used block was supposed to be a C90TLRW (1998). Turns out that it is much older (maybe a 1990/91), in great shape though.