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  1. #1

    Gp1200R carb problem

    Hello. The problem is that the pressure on the return line drops. And it doesn't work without opening the choke handle. Everything can be seen in the video. I found the topic of incorrect primer installation, it says that the primer was installed on the return line and the fuel was pressurized into the carburetor. I have a primer on the feed line after the filter. Can it suck in fuel through it?
    in the video I tried to change the limiter on the return line. The difference is only in the readings of the manometer. There is no difference in driving performance.
    Compression in all cylinders is different, but I believe that this is not the reason.

    Carburetor settings H1.3 / 4 L1.1 / 4 Pop off 45. Neddle 1.5 returne line 95 and 67.5 size



  2. #2

    Join Date
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    It sounds to me like a fuel delivery problem. Have you tried bypassing the fuel selector? Have you pulled the sender unit from the tank and inspected the fuel inlets? Have you replaced the fuel filter? What other mods have been performed on this ski?

    Mike

  3. #3
    Quote Originally Posted by TwoGP12s View Post
    It sounds to me like a fuel delivery problem. Have you tried bypassing the fuel selector? Have you pulled the sender unit from the tank and inspected the fuel inlets? Have you replaced the fuel filter? What other mods have been performed on this ski?

    Mike
    Thank you for your answer. Yes, I understand that there is not enough fuel. I have not yet removed the tube from the tank. but I blew into them and had no problem.

  4. #4
    He took out the flask from the tank, checked everything, examined it. I checked the tubes for vacuum. No problem anywhere.

  5. #5

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    I dont have primers but i would not have the primer on on the supply (suction) side of the fuel line...very easily could be suckling air...that ski should run on two functional fuel pumps (because you must have done fuel pump balancing mod (I use 87.5 at the tank))...plug the primer line and try...yes, primer should have a built in check valve, but things fail.

    At idle on the trailer.
    87.5 on a 1200 will give enough volume for 6 psi
    87.5 on a 800 (two pumps) will give enough volume for 3psi and run fine
    77.5 on a 800 puts you around 5 psi with just two pumps, basically same carbs as 1200.
    An stating the ovious, pushing a xl800 at 50mph take's the same HP/fuel as pushing a 1200 at the same speed. (+/-5%)

    As for volume, about a cup at the tank out of the return line per min...from memory, if the storm does not mess with us, I maybe able to recheck this weekend on the cup.
    Last edited by Crazypirate; 07-29-2020 at 05:46 PM.

  6. #6
    Quote Originally Posted by Crazypirate View Post
    I dont have primers but i would not have the primer on on the supply (suction) side of the fuel line...very easily could be suckling air...that ski should run on two functional fuel pumps (because you must have done fuel pump balancing mod (I use 87.5 at the tank))...plug the primer line and try...yes, primer should have a built in check valve, but things fail.

    At idle on the trailer.
    87.5 on a 1200 will give enough volume for 6 psi
    87.5 on a 800 (two pumps) will give enough volume for 3psi and run fine
    77.5 on a 800 puts you around 5 psi with just two pumps, basically same carbs as 1200.
    An stating the ovious, pushing a xl800 at 50mph take's the same HP/fuel as pushing a 1200 at the same speed. (+/-5%)

    As for volume, about a cup at the tank out of the return line per min...from memory, if the storm does not mess with us, I maybe able to recheck this weekend on the cup.
    balancing mod I have done. return line 95. I also tried to install 67.5 since I do not have other sizes of jets at hand. the whole situation is on the video. at 95, the pressure is only 3-4 a should be 6. at 67.5, the pressure is 6. but there is no difference in engine operation.
    there seems to be insufficient fuel when looking at the return line pressure. but it can be small only in two cases. the first is air from the gas tank, the second is too much fuel going into the carburetor. all fuel lines are vacuum tested, no fuel leaks anywhere. I set the primer differently. tomorrow I'll go test. there is also a problem of high speed on the trailer, more than 5 K. you have to close the air intake to lower the speed. with what it is connected I do not understand.

  7. #7

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    You can not test high engine speed on the trailer..Means nothing..I don't under stand the last sentence..Closing intake??..a run away rpm is caused by vacuum leak after throttle plate.. (gasket, fuel pump pulse line off, throttle plates not closing, or extremely lean to make it diesel)..pull return line off the tank and see if you get you cup of return fuel per min...also there is a check valve off the tank that that prevents the tank from being under too much vacuum (it vents the tank)..How full is the tank?

  8. #8
    Quote Originally Posted by Crazypirate View Post
    You can not test high engine speed on the trailer..Means nothing..I don't under stand the last sentence..Closing intake??..a run away rpm is caused by vacuum leak after throttle plate.. (gasket, fuel pump pulse line off, throttle plates not closing, or extremely lean to make it diesel)..pull return line off the tank and see if you get you cup of return fuel per min.
    no idle speed when working on a trailer. when the engine is started it immediately develops 5-6 rpm. so that the rpm drops to idle, I have to move the choke knob to the extreme position and then the engine rpm drops to idle.
    the engine is just assembled. carburetors too. the impulse lines are installed correctly. there should be no air leaks between the carburetor housing and the engine.

  9. #9

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    You have a vacuum leak, after throttle plate..Pluse line off, wire or hose sandwich, between carb mount base, gasket missing/flipped,,When throttle is released, it should go to idle in less then a couple of seconds, from any rpm.
    Can't have rpm runaway with out air getting around throttle plates.
    Last edited by Crazypirate; 07-30-2020 at 05:45 AM.

  10. #10
    Thanks. Check tomorrow. I will write after verification.

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