GP1300r 2003 jet boat conversion Atmospheric pressure sensor question..
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  1. #1
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    GP1300r 2003 jet boat conversion Atmospheric pressure sensor question..

    Hey guys, i have done my homework trying to find out where the atmospheric pressure sensor is installed, located and have no idea whatsoever, even with the user manual (some of the diagrams are very complex, jamming too much info on one page)
    I bought this Gp1300 for 500$ blown up in pieces and engine only. Have rebuilt from ground up and am on the home straight, i have installed the olll girl into a 3-meter alloy hull, 5mm thick and 12mm plastic. But i am just unsure on what the how to do with the APS.... Could anyone please give me a bit of advice on where it should be installed? If it was on the frame of the jetski i have no idea. Also, what is the purpose of the APS? Is it similar to a car maf sensor?
    Since i have started a thread here i may as well ask the one other question i have, which is about the cooling. I am going to be happy just running stock standard cooling here, from what i have seen in the user manual, the is only 1 inlet, and the rest of the pipes/hoses, (bar the 2 that come out of head and straight into exhaust) go straight out to pisser/s. Which is 4 pipes/hoses altogether? 2 small ones, 1 intermediate size pipe/hose, and the big mama coming out near the end of the stinger. Is this correct??? Seems like alot of hoses going to pisser...? Me old Js550 was different to that. Obviously completely different engines...
    This machine is running a d plate, am planning on ball valves on everything to adjust pressure/temperature as i am running a much bigger jet unit/pump compared to the original Yamaha unit/pump.
    Can anyone tell me what maximum psi should be at any point in the system? And what is the ideal exhaust temperature i am trying to achieve?

    Thanks for any help, I am on the home straight and gunning for christmas/new years, If i get this honey running in time she will be a goodie!!!
    Cheers, Rhys

  2. #2
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: GP1300r 2003 jet boat conversion Atmospheric pressure sensor question..

    Originally it was the front compartment near the ECU.

    It looks like Yamaha was avoiding emi interference by mounting
    some of the important electronics in the front of the ski.

    So mount the ECU and APS far away from the spark plug
    wires and use resistor plugs.

    The air pressure sensor is a barometer. There is also an
    air temp sensor on the flame arrestor. Keep the engine
    compartment well ventilated with air vents to allow air
    in and also out. Heat inside the engine compartment kills
    horsepower.

    Quote Originally Posted by Rhys View Post
    i am running a much bigger jet unit/pump compared to the original Yamaha unit/pump.
    Danger Will Robinson!

    Increasing the load (with a larger pump) will increase combustion
    temperatures. Look in the manual for what rpm the engine made
    peak HP at, and if you measure less, stop your testing and repitch
    the impeller.

    On a 1300, increased pump loads will likely melt down the rear cylinder.

    Quote Originally Posted by Rhys View Post
    Can anyone tell me what maximum psi should be at any point in the system?
    I measured 50psi (flowing water pressure) in between the pump and
    engine of a 1100 wave raider. Your pressure will depend on your
    pump set-up, but it should not be less.

    Quote Originally Posted by Rhys View Post
    And what is the ideal exhaust temperature i am trying to achieve?
    My stock ZXI 900 had a cool 900 degrees, but the temperature you
    measure will depend a lot on where you measure it. Location is
    important. Too close to the piston and the fuel that is short circuited
    out the exhaust can artificially cool the egt.


    Bill M.


    What did you decide for a premix ratio? I strongly recommend a
    Yamaha oil at 20:1.
    Horsepower == Speed, RPM != Speed



  3. #3
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    Re: GP1300r 2003 jet boat conversion Atmospheric pressure sensor question..

    Ohhh yeap, so so long as APS is far away from spark and box it can basically just mount any old place in the engine bay? Yes, my plan is to get a psi measurement with the cooling and use a ball valve after sand trap to restrict any excess pressure.. If it is true with what i said about having pretty much 4 pissers then i prolly wont hesitate to put ball valves on them all to find the optimum running temp if i can. I would really sleep easier at night tho if someone posted a basic simple diagram of how the stock cooling should all flow, just to confirm what ive read and put my mind at ease..
    I have done away with the factory oiler, you are saying 20:1 but that sounds hugely rich??!! from what ive read on these forums people have only ever run 45:1 to not clog up fuel injectors... Or am i on the wrong track here. 20:1 is a **** load of oil!....

  4. #4
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    Re: GP1300r 2003 jet boat conversion Atmospheric pressure sensor question..

    I think he meant 50-1 or at least I hope he did.
    Y'all know me, still the same O.G. but I been low-key
    hated on by most these &^$$@s with no cheese, no deals and no G's, no wheels and no keys, no boats, no snowmobiles, and no skis, mad at me cause I can finally afford to provide my family with groceries

    WWSRD , What would Speed Racer do ?

  5. #5
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: GP1300r 2003 jet boat conversion Atmospheric pressure sensor question..

    Quote Originally Posted by Rhys View Post
    Ohhh yeap, so so long as APS is far away from spark and box it can basically just mount any old place in the engine bay?
    Yes

    Quote Originally Posted by Rhys View Post
    Yes, my plan is to get a psi measurement with the cooling and use a ball valve after sand trap to restrict any excess pressure.
    Sounds like you are making your cooling line setup
    more complicated than necessary for really small HP
    gains

    Triples need water boxes with large inlets and outlets,
    and Yamaha water boxes do that better than Kawasaki.

    Besides, a dry waterbox will most likely cause a bogg
    on acceleration.

    Quote Originally Posted by Rhys View Post
    20:1 is a **** load of oil!....
    If it prevents a seizure while you are testing your setup,
    it is exactly what you needed. If your new pump setup doesn't
    allow the engine to rev out near peak hp, you are risking engine
    reliability (crank shaft twist will advance the ignition timing on
    the rear cylinder).

    I used to believe that was a lot of oil, but that changed with
    my experience racing Kawasaki X2's in the last 6 years.

    I could give you reasons, share magazine dyno tests, but
    why?

    More oil is just more lubrication, less friction, less wear, and
    good oils don't smoke or foul your plugs.


    Bill M.
    Horsepower == Speed, RPM != Speed



  6. #6
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    Re: GP1300r 2003 jet boat conversion Atmospheric pressure sensor question..

    What about the injectors tho? I have done away with the factory oiler. I would run a richer mix but from what ive read, most dont go lower than 40.1 that have no oiler... I assuming in case it clogs up injectors..

  7. #7
    PWCToday.com Is My Home Away From Home wmazz's Avatar
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    Re: GP1300r 2003 jet boat conversion Atmospheric pressure sensor question..

    40:1 is 2.5% oil, and 20:1 is 4.7% oil. That means you have 95 to 97%
    of gasoline (or a solvent).

    It does mean your fuel will be 2.5% leaner.


    The only things that are unreliable with oil injectors are the oil lines do not
    last forever, the owners forget to fill the oil tank, and SeaDoo oil injector
    pumps tend to loose the oil seal. But on SeaDoo's when that happens they
    run oil rich.


    That said, I have never tried 20:1 through a fuel injector before. But I
    don't foresee a problem with it.



    Bill M.

    My main concern is your reliability during initial testing. I have seen an X2
    engine not seize (while running 20:1) after an oversized impeller was installed.

    But 20:1 doesn't eliminate the possibility. You must recognize the problem
    and take action.

    A common mistake is to rationalize the problem away, by telling your self
    that if you avoid wot, you can ride for the rest of the day.

    That X2 eventually seized, and when it seized, it seized harder than any
    engine I have ever seen.

    Besides the aluminum on the cylinder wall, it twisted the driveline, pushed
    the crankshaft forward through the main bearings. When the driveline twisted,
    it bent at nearly a 90 deg angle, and slammed through the bottom of the
    hull causing the X2 to sink. LOL. It lasted about a month before it seized.
    Last edited by wmazz; 12-04-2022 at 08:24 PM.
    Horsepower == Speed, RPM != Speed



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