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  1. #1

    787 Carb Adjustments/Mods & Performance

    Hey everyone! Well I dont know if Im the last one around still using a 787 engine, but I havent got much feedback from other forums so I gonna try here.

    1997 SPX, 787. Engine All stock but oil injection delete, and aftermarket flame arrestors. Well looked after. 91 Octane. 115 HRS on new build.

    Now since I got this machine, its been a PIG to try and tune out this terrible dead spot it has, anywhere from 3800-4600 is just a dog, missing, carrying on. Now someone said its from those flame arrestors, and poor jet transitioning between high/lows.. But Im willing to bet theres gotta be better tuning methods and others out there that have done that simple mod. I rode my friends machine and it has way better throttle responce, smooth all the way through most of the RPM.. Mine doesnt run like that at all.

    My WOT plug chops are pretty good, low end is always rich. I turn about 6650 RPM.

    So Im wondering if theres anyone that has good carb setups/specs for this type of mod? Or any other info that might help me tune out this issue. Hopefully I can get this pig running better, and thanks in advance.


  2. #2

    Join Date
    Sep 2009
    Location
    n.j.
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    457
    you are far from being the last 785 rider! i have the same pwc, which flame arrestors are you using? did you delete the stock choke set also?

  3. #3

    Join Date
    Sep 2009
    Location
    n.j.
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    457
    make sure that your fuel lines are no longer the grey ones. make sure you fuel selector is clean, replace it or bypass it. carb rejet as follows- stock mains, 75 pilots, 80gram springs, 2.0 needle and seats.

  4. #4
    Quote Originally Posted by jersey785 View Post
    make sure that your fuel lines are no longer the grey ones. make sure you fuel selector is clean, replace it or bypass it. carb rejet as follows- stock mains, 75 pilots, 80gram springs, 2.0 needle and seats.
    Man everythings messed up on this forum right now. Odd..

    Alright, my bad. I also have choke delete, primer install.. I cant verify if its been taken up one bore or not when it was rebuilt, It was done before I bought it.

    First thing I did was rebuild the carbs, chuck those junk fuel lines in the trash and cleaned it all up. I started it once with my return line off, and theres LOTS of fuel flowing.

    So Youd suggest stock jets EVEN with the flame arrestors and choke deletes? If the engine was one bore over stock would that matter? And oil injection delete wont require larger jets either?

  5. #5

    Join Date
    Apr 2005
    Location
    Upstate NY
    Posts
    37
    Sticky rave valves will cause some hesitation. Have you cleaned them since the rebuild?

  6. #6
    Quote Originally Posted by revhardSPX View Post
    Sticky rave valves will cause some hesitation. Have you cleaned them since the rebuild?
    I usually clean them every season. I didnt this spring because they seemed to be pretty free. I can try that again as well.. I would think I should get more then 6700 RPM. Its got a skat trak 17/22 swirl, top loader grate. But still.. Maybe its just too rich.

    And I dont think I have a black needle spring in there either, IIRC its a silver one. I wonder if the fuel pressure is too high and flooding it out at certain lower RPMs..

  7. #7

    Join Date
    Sep 2009
    Location
    n.j.
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    457
    did you use mikuni diaphrams or after market? you may be flooding your carbs by the tip of the diaphram opening the needle, causing hard starts, load up, then clears once your secondary kicks in( hesitation). yes, stock main jets but 75 pilots and you should use the 80gram springs with 2.0 n/s. are the oil ports sealed?how about the other choke plate rod hole? is that sealed?

  8. #8
    Quote Originally Posted by jersey785 View Post
    did you use mikuni diaphrams or after market? you may be flooding your carbs by the tip of the diaphram opening the needle, causing hard starts, load up, then clears once your secondary kicks in( hesitation). yes, stock main jets but 75 pilots and you should use the 80gram springs with 2.0 n/s. are the oil ports sealed?how about the other choke plate rod hole? is that sealed?
    Mikuni parts Only. I need to check the float arms thats on my to do list, and Im gonna order the stock jets as soon as I can and see what pilots are in there. Now, where would you start with the adjuster screws? Fat to start is usually whats best obvsiosly. Do you run aftermarket FA on your machine? I wonderd about my pop off too..

    I JUST put in a new stator this year, new OEM coil, plugs ALL the time, new NGK plug boots. Amsoil Oil.. I try to look after this thing but its starting to irritate the **** outta me.

    All the holes from choke and oil are blocked off.

    IIRC there is a 72.5 in my MAG carb and a 75 in the PTO. The high speeds are two sizes up which IIRC is 147.5. Adjusters closed. I bet its my springs causeing issues.
    Last edited by 6000 SSEi; 07-20-2010 at 04:53 PM. Reason: Forgot to answer something

  9. #9

    Join Date
    Sep 2009
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    n.j.
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    457
    you still haven't said what your needle and seat are. trust me and stick to my specs. It's what i'm using and it was recommended by quite a few people and it works. oh btw, dump that skat swirl and go back to stock or a solas xo. you don't race so there's really no benefit to having the swirl, it actually scrubs off top end. and you mentioned 91 octane, is your head milled? I have the lows out 1 1/4 turns and the highs about 1 turn out. start there and then do a plug chop.

  10. #10
    To be honest, I forget what needle and seat I have. I'll see if I can get them off tomorrow to check. The skat track seems to work really well, and I've never had to pick weeds out which is great. I'm into some really weedy places sometimes. And altough I don't race or anything, i do a lot of playing around, short distance runs, and playing in the big waves in lake Ontario. Is the skat trak no good for that? It also came with the machine. And what do you mean by it scrubs? I appreciate all the replies and input. I just want to know everything about everything. Hopefully you don't mind all my questions.

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