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  1. #1

    How to make older two-strokes more fuel efficient/quieter

    There is no shortage of information on how to make a jet ski faster, we all want faster skis, but there seems to be little information on how to make one more fuel efficient/quieter...without ruining performance. I mentioned in another post how Group K switched out 40mm carbs for 38's on a '97 GSX and got way better fuel efficiency without really hurting performance. For me it's not so much about the money as it is about always having to get gas (where my new STX sips gas). Also, the loudness of a two-stroke can be a little much when I'm trying to convince kayakers that I'm not a monster because I love jet skis, anyone have ideas on how to quiet one down, again, without killing performance.
    Thanks again for all your help.

  2. #2
    GGG's Avatar
    Join Date
    Sep 2009
    Jersey Shore
    Im not sure about fuel efficiency but 951 seadoos have multiple in-line resonators on the exhaust that should quiet things down

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada
    I like the direction you are trying to go in

    Fuel efficiency is a tough one. Better carbs might help a lot or only a little. Depends on what you are starting with.

    The Direct Injection fuel injected engines tend to have good full economy. Diagnostics are very different from a carb engine, and some models have reliability or repair cost concerns.

    The modern method is to install a 4 stroke engine into the old hull. These conversions tend to be fairly good with fuel consumption, as long as you don't put a huge HP engine in, or use all the power all the time

    The SeaDoo 4-Tec engines seem to be similar in weight to a large 3 cylinder 2-stroke engine, so the hull handling doesn't change much after the engine conversion is installed. Doing such a conversion is not a drop-in easy project, but the number of successful conversions keeps rising.

    The 4-stroke engines generally are quieter, especially if the exhaust silencers are retained.

    A turned down exhaust exit can reduce sound levels, especially at idle and low speeds. Aiming the exhaust downwards into the water reduces the noise. If the exhaust tip is positioned properly, there is minimal impact on engine power at speed.
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  4. #4
    GGG's Avatar
    Join Date
    Sep 2009
    Jersey Shore
    I like seadoo and mercury's direct inject because it injects pressurized air with the fuel which atomizes it to the max. On seadoo, you use 2 gallons per hour less at wide open throttle than you do with a carb setup on the same motor

  5. #5
    Thanks for all the tips. I'd like to stay with the old two-stroke because they are cheaper to work on. I'm hoping to buy a ski in good shape and make it a bit better, not dump tons of cash into it. I'll probably stay away from FI for the same reasons as not wanting another 4-stroke...they're too expensive to fix and the reliability of the electronics. I'll probably buy an older GTX (96-7), but am also looking at the GSX, Kawi STX, and maybe even a GPR or an Ultra, all with carbs.
    Basically what I need is a fairly fast, reliable older ski. I'll probably try to make it faster, but better fuel economy and less noise would be a nice bonus. I was thinking you could line the hull with the same stuff that outboards use, or maybe wrapping the exhaust in something that wouldn't be a pain to work around.
    And as for fuel economy, are there impellers that would greatly aid fuel economy and maybe even the holeshot at the same time? On my boat I changed the prop size and while I lost a little off the top (1-2mph), it basically jumped out of the water when you pinned it and seemed to get better fuel economy.

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