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  1. #1

    Old School conversion

    You can add this to your collection of conversion projects. I only found you guys the other day, which is a shame because I would have done a few things differently based on your combined experience.

    I am three weeks out from her christening, with mostly varnish work left to do.

    Engine concerns at the moment are mainly centered around idle speed (in the driveway she idles at 2100 rpm). If I even touch the throttle she bumps up to 3000 rpm and won't come down. In the water she idles at 1850, if I bump the throttle she jumps up to 2750 rpm and then settles back down after about ten seconds. I am not shure why this is happening or if maybe it is normal even (although that would be odd).

    Any advice?

    Last edited by oldschool; 05-03-2008 at 02:52 PM.

  2. #2
    Moderator RX951's Avatar
    Join Date
    Apr 2005
    San Antonio, Texas
    Welcome to the forum !!!!

  3. #3
    Vern's Avatar
    Join Date
    May 2005
    Grand Haven, MI
    Cool and unusual project ... give us some details? Length, propulsion system, speed, rpms, etc.

    Idle ... 2300 out of water and 1850 in water are normal. The fact that idle does not drop immediately is not really a major problem, but I would pull the SC to TB hose and inspect the throttle body to make sure it is not gummed/salted up and that it snaps back easily (maybe detach the throttle cable to isolate the behavior of the TB and return spring function). If that looks and behaves well, then I would double check the throttle cable itself ... routing, is it bent/kinked anywhere or internally sticky.

  4. #4
    Duke's Avatar
    Join Date
    Jul 2006
    Welcome to the forum!!!!! You found the right place to help you on the 4-tec motor.

    Funny thing is we have already seen a few spy photos of your project!! Looks great BTW.

  5. #5


    She is running a 2003 185 SC engine, with a mercury I/O engine's heat exchanger for a cooling system (which I may rip out and swap with open loop cooling). The boat is 17 feet in length and a little less than 6 feet wide. A shallow deadrise hull with two ventilated steps in the aft third to reduce wetted surface area is my own design. The whole boat with a full load of fuel is just over 600 pounds in weight (I do expect to go fast). The hull design means she will prefer clean water, and heavy chop and wake jumping are definately out. She can seat two adults and two kids, and pull an inner-tube, maybe a skier.

    Total investment appx. $ 10,000

    I have only had her in the water once so far, just to see if she floats on her lines and to check the jet drive.

    Places where I may get in trouble...
    I have totally redesigned the jet intake. I studied the knowledge base of the guys who race jet boats on the feather river here in CA. They run huge engines (400-600hp) and Berkely or custom pumps. Their boats can run all day at well over 100 mph. Things I gathered from them include moving the intake as far aft as possible to reduce air ingestion, oversizing the intake to reduce the likelihood of cavitation, a result of pump starvation. Liberal use of hull strakes to break up the water tension on the bottom of the hull in areas not directly ahead of the pump intake. I may find that I will have to change the prop pitch and the nozzle size to get the most out of the pump.

    The boat is undoubtedly a "proof of concept" in many ways. Only the river will tell if I am right or wrong. In a few weeks we will know. While I am new to jet boats and SeaDoo engines, this is the 9th wooden boat I have built.

    This is the end of a long road for me. The boat has taken up all my free time for almost four years.

    Thanks for the warm welcome.
    Last edited by oldschool; 05-03-2008 at 02:55 PM.

  6. #6
    The ski's have taken a "backseat" to the Corvette DarthAWM's Avatar
    Join Date
    Nov 2007
    Odessa, TX
    Welcome, to the forum. What an awesome home for a 4-tec motor. I hope it works well for you.

  7. #7
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    Good stuff man!! Keep us posted and if you need anything just ask. We have the best of the bunch....

  8. #8
    cheatin' piston popper addicted's Avatar
    Join Date
    Jul 2006
    north jersey
    That's cool

  9. #9
    Hydrotoys's Avatar
    Join Date
    Jul 2005
    Mesa, AZ

  10. #10
    fabrication guru rapidacceleration's Avatar
    Join Date
    May 2005
    Lake Travis austin, TX
    this thing is awsome.. i love that wood look. pure classic look with a touch of new technology...

    if ya need help with anything, pm me...

    keep the pics coming...

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