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  1. #1

    787 efi project, (not rfi)

    working on converting my carb 787 to efi using microsquirt efi like others have done.
    Using a combination of seadoo parts that i have at the shop to build the motor with what i have. Rfi casses for the case cooler, carb cylinders, stock pipe with ecwi, buckshot head with 43cc domes, yamaha fx ho mikuni 40mm throttle bodies, yamaha 1300r efi fuel injectors, and gm/ mercury marine coils.


    starting to come to a couple options i can do with the engine that will possibly improve the life of the engine mainly with oiling. Looking for info and or opinions and any thoughts or ideas others might have.

    im planning on keeping the stock oil injection but switching to the 951 Di oil pump since it has 3 outputs instead of just 2. I am going to run the 2 lines to the stock location on the rotary valve cover for the oil injection, then take the third line and split it off to various locations. 1 to the ballanace shaft gear, 2 to a spot on the rotary valve cover to supply oil to lubricate the actual rotary valve between the case and the cover, and 3 to suply oil directly to the crankshaft bearings through drilled passages in the cases.

    just trying to eliminate some of the failures that i see in these engines working on them everyday. then again im dealing with salt water, neglect, improper flushing, and sinking.


  2. #2
    still workin on this project looking further into it. Someone who knows about fuel injection and rotax performance. since there is 2 versions of the 787 the carb model and the rfi model. What is better and has the possibility of making more power? port injection in the throttle body injecting fuel/ air mixture into the crank case, OR using the rfi cylinders with the injector in the 3rd transfer port?

    essentially taking an rfi engine and running it with a different programable ecu (microsquirt) and running it with individual 46mm throttle bodies say from a 951 di.
    reason for not running straight rfi engine and electronics is because of all the problems associated with it, and it doesn't allow for mods. i plan on cylinder and case porting as well as raising the compression.

  3. #3
    Tincorus Maximus
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    Straight RFI engine has advantages, but with the injectors where they are, you can't run the stock carb exhaust. RFI exhaust dumps down the right side of the boat, and will not mate up to your waterbox properly. Still think you ought to run the RFI throttle body and intake, and not the two WAY oversize throttle bodies, as your torque curve will likely be non existent below 6k, and throttle response may be, um, lacking. Really like your oiling mods, though!

  4. #4
    so... spoke to someone more educated than i at 2 stroke shop. they do some killer 2 stroke motorcycle work. guy told me they did some efi race ski's and worked really well. that big oversized throttle bodies can be used if the rest of the mods to the engine suit the diameter. and that replacing a 40mm i series carb with a 40mm throttle body would be pointless and yield no better results than a carb, performance wise. but... a 787 with sbn 44's or 46's does very well. so a ported 787, with bump in compression, and few other mods should take well to the 951 di throttle bodies. that and their the cheapest throttle bodies of that size ive found. only paid 50$ for mine. wanting to run 2 seperate throttle bodies over the rfi single throttle body so there is no disturbance in the air from 2 cylinders pulling from one source. so its technically 2 seperate cylinders running together sharing the crankshaft and a single pipe.
    just recently found out the 3d rfi pipe is a dry pipe. looking into getting one just to see if there is any internal differences compared to other oem seadoo pipes. the 3d rfi pipe would allow me to run rfi cylinders with the injectors in the transfer ports. still yet to determine if transfer port or intake port injection is better. heck look at the yamaha 1300 efi its in the throttle body and its one 40mm throttle body per cylinder.
    for the microsquirt im goin with a 36-1 trigger wheel shrink press fit on the mag cup using a 951 di hall effect sensor for the pickup.

    hopefully ill be able to get engine up and running with the ecu on with all sensors atatched and log the engine while riding with a set of carbs to get a base to tune from. hopin this will work.

    there is also a chance with the microsquirt to run map sensor at low rpm, when map signal gets low or unstable the microsquirt programing switches to reading a mass air flow sensor along with tps and rpm to determine load.

    im just interested to know for the 159 degrees the rotary valve is open should the injector be spraying or pulsing the whole time? and how the heck do i determine this.

  5. #5
    IDoSeaDoo's Avatar
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    Any news on this?

    Quote Originally Posted by slociviccoupe View Post
    so... spoke to someone more educated than i at 2 stroke shop. they do some killer 2 stroke motorcycle work. guy told me they did some efi race ski's and worked really well. that big oversized throttle bodies can be used if the rest of the mods to the engine suit the diameter. and that replacing a 40mm i series carb with a 40mm throttle body would be pointless and yield no better results than a carb, performance wise. but... a 787 with sbn 44's or 46's does very well. so a ported 787, with bump in compression, and few other mods should take well to the 951 di throttle bodies. that and their the cheapest throttle bodies of that size ive found. only paid 50$ for mine. wanting to run 2 seperate throttle bodies over the rfi single throttle body so there is no disturbance in the air from 2 cylinders pulling from one source. so its technically 2 seperate cylinders running together sharing the crankshaft and a single pipe.
    just recently found out the 3d rfi pipe is a dry pipe. looking into getting one just to see if there is any internal differences compared to other oem seadoo pipes. the 3d rfi pipe would allow me to run rfi cylinders with the injectors in the transfer ports. still yet to determine if transfer port or intake port injection is better. heck look at the yamaha 1300 efi its in the throttle body and its one 40mm throttle body per cylinder.
    for the microsquirt im goin with a 36-1 trigger wheel shrink press fit on the mag cup using a 951 di hall effect sensor for the pickup.

    hopefully ill be able to get engine up and running with the ecu on with all sensors atatched and log the engine while riding with a set of carbs to get a base to tune from. hopin this will work.

    there is also a chance with the microsquirt to run map sensor at low rpm, when map signal gets low or unstable the microsquirt programing switches to reading a mass air flow sensor along with tps and rpm to determine load.

    im just interested to know for the 159 degrees the rotary valve is open should the injector be spraying or pulsing the whole time? and how the heck do i determine this.
    Damn interesting concept. Did you get it to work?

  6. #6
    I had a squirt running a 785 motor about 10 years ago. It ran great.

  7. #7
    IDoSeaDoo's Avatar
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    how did you program the fuel maps?

    Quote Originally Posted by whittlebeast View Post
    I had a squirt running a 785 motor about 10 years ago. It ran great.
    Where did you find how to program the fuel map? Did it compensate for temperature or MAP? What would a system like this cost if I'm starting from scratch?

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