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  1. #1
    philip_gpr's Avatar
    Join Date
    Dec 2005

    How to get more fuel to a BB EFI GPR

    How to get more fuel to a Big Bore EFI GPR

    The GP1300R uses a fuel system that is very similar to the one used in the SHO. Which is also very similar to the one used in most motor vehicles.

    The role of an EFI Controller

    The EFI injectors feed fuel into the throttle bodies. The injector is basically an on off switch. The EFI system controls how much fuel is being provided by controlling the timing and duration the injectors are in the open position.

    The Riva and R&D EFI controllers provide additional fuel to the motor by lengthening the duration the injector is in the open position. Unfortunately these controllers are limited in how much additional fuel they can provide. This has placed a practical limit on the size of ported motor that can be used with the OEM GPR EFI system to 1390.

    In order to maintain the OEM EFI system with a motor larger than 1390, an additional method for richening the fuel mixture will need to be used. This is the same issue that the 4 stroke motors have when raising boost or when adding aftermarket turbo chargers.

    The components of the GPR and SHO fuel sender

    The fuel sender is comprised of 3 pieces of plastic that snap together to make a single unit. This unit is then bolted to the top of the gas tank.

    The electric fuel pump mounts inside the middle plastic section of the fuel sender. The fuel pump feeds fuel up a black fuel line to a fitting located on the top of the fuel sender.

    In addition to holding the fuel pump in place the middle plastic section includes a built in fuel pressure regulator valve. This regulator is round, is about inch in diameter and is silver in color. This valve limits fuel pressure to 45 lbs. When this valve opens excess fuel is routed through a 2nd black hose to the bottom of the fuel sender.

    Adding an external fuel pressure regulator

    It looks like it would be an easy process to disable this internal pressure regulator. Once this was done, an external regulator could be installed in the fuel line that feeds the throttle bodies. These external regulators require a return line to be used. This return line would then route excess fuel back to the fuel tank. This return line would require a fitting to be added to the top of the fuel sender.

    By installing an external regulator you could then control what fuel pressure is being used. By raising the fuel pressure, you can richen the fuel mixture.

    How high the fuel pressure can be set would be limited by what pressure the OEM fuel pump is capable of generating.

    Adding an aftermarket fuel pump

    If additional pressure is needed, the OEM fuel pump can be replaced with an aftermarket high pressure pump.

    R&D offer a replacement fuel pump for the SHO. In all likelihood this same pump will fit the GPR fuel sender.

    R&D also offers a pressure gauge and return line set-up for the SHO. These same parts would probably work fine on a GPR.

    Many aftermarket automobile shops also provide fuel pumps, gauges, lines and fittings

    On the R&D web site you can see the products they are offering for the SHO in order to do modification I am describing here. I suspect many of their products would be plug and play for the GPR.

    By applying these concepts to a GPR we can remove the displacement limitation of 1390 for an EFI ski. By increasing fuel flow 10% this could allow us to use a displacement of up to 1530. A 15 % gain would take us up to a displacement of 1600.

    As a final note, anyone looking for a shop to build a ski using these concepts I have discussed in this post should consider WFO. Richard is one of the few individuals that has experience building a GPR using an aftermarket fuel pump and regulator.
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  2. #2

    Join Date
    Mar 2008

    very interesting

    very good reading.a 1600cc gpr is what i want some day.maybe when the gpr guru's have this figured out a little better imight have to put this into my budget.

  3. #3
    dlamazing's Avatar
    Join Date
    Apr 2009
    miami fl
    thats good your in the rigth direction if any of you need help on this i have it already done send me a pm for info

  4. #4
    Hydrotherapy's Avatar
    Join Date
    Sep 2006
    The Rock
    Quote Originally Posted by dlamazing View Post
    thats good your in the rigth direction if any of you need help on this i have it already done send me a pm for info
    welcome to GH

    why not share your finding with us all,even if the reader will not use it it would make interesting and educational reading for all

  5. #5
    Chrisrokc's Avatar
    Join Date
    Apr 2006
    Oklahoma City, OK
    Quote Originally Posted by dlamazing View Post
    i got a high volume fuel pump for the gpr disabled internal regulator running a external fuel pressure regulator custom fuel rail i made to a true return style system since every 1 hasent noticed that cylinder 3 always runs lean due to low fuel pressure the end of the stock rail! so mines maintains contant pressure througth the entire rail by having the efi set at max on the top end dail set fuel pressure it runs on the sweet spot thats all you need! so if you 1390s or 1500s ppl need more fuel let me know i sell you the whole set up needed to run efi on a bigbore

  6. #6
    dlamazing's Avatar
    Join Date
    Apr 2009
    miami fl

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