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  1. #1

    Unhappy GP1200r only will suck fuel from the fuel lines.

    Hello all.

    I have a GP1200r that was not running when I got it so i have rebuilt the top end and the carbys with all new parts.

    The problem I'm having is fuel delivery. If i put a boat bulb in the line and prime the line it fires up no choke streight away and runs but will drain the fuel from the fuel filter and fuel hose but will not pick anymore up outa the tank.

    1. Fuel lines are new ( zip tied on atm getting hose clamps next week end)

    2. Fuel sender is not blocked blew air through all in/outlets.

    3. Took slap off of the fuel sender.

    4. Fuel lines are on correct. Main feed goes to carby 1 and return is on carby 3 ( rear carby )

    5. Air separator disc things in the pumps are not creased they're all new.

    6. All gaskets and needle and seats are new.

    7. 3x new postons and bearings and a full top end gasket set.

    8. Honed and cleaned. Also noticed all cylinders have been ported.

    9. Oil pump delete and sender tripped.

    10. Fuel tap has air come through it on res/on but when off its blocked like it should be.

    11. New NGK plugs.

    12. 55L premix fuel in the tank.

    13. Return line doesn't have fuel comming out of it.

    If we keep priming the bulb constantly we can rev it but if we don't prime it after about 30secs of idle it runs the lines dry and if we rev it without priming the bulb it runs the lines dry within seconds.

    Is there a trick to get the carbys all primed up?


  2. #2
    jeffg426690's Avatar
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    Two things to maybe think about:
    Did you do the fuel return mod on the carbs? (It's in the How-to stickies in Yama 2-stroke sect here), possible your returns are hosed up in the carbs and also just a good mod for preventing creased check valves in the carbs down the road.
    Have you checked your fuel vent check valve. It may be stuck closed which will create a vacuum in the fuel system and make it difficult for carbs to pull fuel. The check valve on the return is just above the fuel pickup and should allow air into the tank but not out.
    Let us know how you make out w it

  3. #3
    Myself's Avatar
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    While the carbs were apart did you verify the returns were NOT blocked? I've seen them so bad corroded before that I had to heat the fitings and pull them out of the aluminum to redrill the blocked off passages!!

  4. #4
    Adam's Avatar
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    Do you have a 95 main jet in the return line ? If not the carbs will suck air back from the fuel tank and stop the engine.

  5. #5
    Hey guys all holes and hoses were clear I blew the carbys completely out with the air compressor. Dunno about the 95 it's got standard jets everything is standard

    Also i have not checked that valve hmm I shall do that. Haven't drilled out the return hole and put in a reducer in the line wasent really intrested is doing it...
    Last edited by Trizza1996; 03-24-2020 at 05:14 AM. Reason: Forgot a few things

  6. #6
    jeffg426690's Avatar
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    Quote Originally Posted by Adam View Post
    Do you have a 95 main jet in the return line ? If not the carbs will suck air back from the fuel tank and stop the engine.
    The 95 pilot jet is not for this purpose, it is part of the fuel return mod that Oside Bill came up with: drilling out the teeny/tiny fuel return holes inside the carb body and putting a single restrictor in the return line that approx equates to the combined area of the three small return openings that got opened up. It's a pm type of mod that eliminates return passage issues and is very quick and super easy to do, also eliminates check valve issues inside the carbs.

  7. #7
    Chester's Avatar
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    Go through you fuel system. Check the lines and sending unit for sucking in air.

    Chester

  8. #8
    Chester's Avatar
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    Quote Originally Posted by Adam View Post
    Do you have a 95 main jet in the return line ? If not the carbs will suck air back from the fuel tank and stop the engine.
    Not possible.

    Chester

  9. #9
    Myself's Avatar
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    WHOOPS!! Just reread this.
    Your comment #4.............Lines are backwards.
    Fuel comes in at rear carb with acc pump and exits at the front carb.




    Come on guys! We're snoozing! We're better than this, lol!

  10. #10
    Mike's GPR's Avatar
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    This is why I stick to fuel injection

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