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  1. #1
    kegonsa's Avatar
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    SLT 780 fuel troubles : Fuel Restrictor?

    So I went through over winter and replaced all fuel lines, rebuilt the fuel pump and carbs. All seemed fine this spring and and noticed the difference in response on take off.

    This past week my wife said that when she was out with a friend she noticed it did not take off like it should and topped out at 30. I had taken it out a couple of times and it seemed fine to me, thought it may have been weeds.

    Yesterday while I was out it happened to me. I was hitting about 5000 rpms and was going no where.

    When I got it back I did a compression test and had 125, 125, and 100 on the PTO. After doing some reading and looking at xlints pic I know I dont have a restrictor on the return line. I looked through the lines I took off and there is not one there.

    Are the SLT 780s suppose to have one, if so does any one have one for sale?

    I was going to pull the head, and possible the jug tonight, but it is suppose to storm so I might have to wait.
    Last edited by K447; 07-09-2011 at 08:37 AM.


  2. #2
    kegonsa's Avatar
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    Well I had enough time to get the dome off before the storm. The walls were smooth and in good shape. The head gasket was cracked on both layers on the inner ring and I think that is the cause.

    Any thoughts of what else to check before putting a new head gasket on and testing. I will also try and get pics up tomorrow.

  3. #3
    johnsonmtz's Avatar
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    On the '96 780 engine the restrictor was built into the fuel return nipple so you don't need to worry about that.

    The cracked gasket and low compression on PTO could have been your problem. You'll just have to get on the water and see on that one.

    How did the piston wash look when you had the heads off? Are you certain you had the low and high adjustment screws set to factory specs after the carb rebuild?

    Low speed screws = 1 3/8 turns out

    High Speed Screws
    MAG = 1 1/
    CEN = 7/8
    PTO = 1 1/4

    Verify these settings before you take the ski out again.

    KJ

  4. #4
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Correct, no restrictor in the 780's. They are built in.

    If your head gasket cracked, make sure you have it installed the correct way.

    How about a pic of the piston and gasket the way it was on the cyl?????

  5. #5
    kegonsa's Avatar
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    When I rebuilt I used the settings from Beerdarts post

    SLT780 - Low Speed – 1-3/8
    High Speed – 1-1/8m, 7/8c, 1-1/4p

    The washwas very rich, the person I had bought the ski from had it turned way out. I will try and put some pics some time today.

  6. #6
    kegonsa's Avatar
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    Got tired of studying for my CCNA so I went and took some pics. As you can see very rich. I have not ran through a tank of gas yet since the rebuild, how long does it take for the piston wash to adjust? If you look at the side of the jug and dome you can see carbon build up where the crack was so I hope that is the only issue. I found a fried that has a head gasket so in the next couple of days I will put that on and do a compression test.
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  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Wash will take about 1-2 hrs of riding to form.

    But, if you're getting water inside the cylinder it actually steam cleans the piston. (like a blown head gasket)


    Replace the gaskets, making sure they are positioned correctly, and install the right plugs. I bet you get a good runner then.

  8. #8
    kegonsa's Avatar
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    I just got a head gasket last night and put it on this morning, I now have 125 across the board.

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by kegonsa View Post
    I was hitting about 5000 rpms and was going no where...
    What do you mean by this?

    Was it going at about the right speed for 5000 RPM or was the engine revving without providing much jet thrust?

  10. #10
    kegonsa's Avatar
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    So I replaced the head gasket and got 125 across the board. Test run last night was good. Today it ran fine for a while and then it started back up. It will run fine for 5 min and then it just does not rev like it should. The rev up seems slower and only gets to 4220 RMPS. No warning lights, gas and oil is full.

    Over the winter I did the following
    rebuilt carbs and set to factory specs
    rebuilt fuel pump
    replaced fuel lines

    Every thing seemed to run fine the first couple of times out with out any issues after that.

    so far I have tried:
    new spark plugs BPR8ES set to .26
    cut back the wires and put the boots back on
    Spark looks good
    made sure that cylinders are not getting to hot. I can keep my hands on for about 5 seconds
    Compression is 125 on all three
    inspected the breathers for the fuel line, I do not know how to test them
    put oil on the rim and cap for the gas for a good seal.
    checked the the exhaust and tubing for holes and leaks.

    at this point I cant figure out why it is doing this. Seems to rev fine to about 3400 and works its way to 4220. some times if I let off and get back on it takes off like it should. Any help is greatly appreciated

    K447 I know that I said 5000, I was not driving so that was a guess. by going no where I meant it felt like there was no torque. I never really drive at 4200 but I think the speed was about right. If you are hinting at the pump I dont think that is the case.

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