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  1. #1

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    Question 1996 SLT7 780 Rebuild Issues

    I have been trying to debug a 1996 SLT7 780 for some time now and I am not sure what the next step should be. Any and all help is appreciated.

    I rebuilt the entire engine and carbs and when I started everything up for the first time it was not running correctly. The engine was running off of one cylinder and although it idled well out of the water, when it was under a load, the engine would bog down and die as soon as I opened it up on the water. When I was inspecting the carbs when trying to diagnose I realized the jets were different sizes than the stock carbs should be for a 1996 SLT780.

    I found another set of carbs on ebay from a 1996 SLX780. The carbs have different jetting but where the engine is the same, I assumed it would work the same. The engine seemed to perform better with these new carbs, but it was still not right and my inexperience in tuning carbs led me to believe something was still wrong.

    I found a third set of carbs, this time confirming they were off a 1996 SLT780 and confirmed with my own eyes that the jets were correct. I rebuild this carbs and installed them just last weekend. The pwc fired right up but seemed to be running high at idle. After a few seconds it slowed down but when I would open the throttle the response was not as I would have assumed. It changed pitch with the throttle but not as much as I would have thought. So i confirmed that the front and middle cylinders were running on their own, and they were running high individually as well. I then attempted to run the rear cylinder and it would not fire up. Taking the top of the carbs off and sticking my hand over the choke plate I was able to confirm that fuel was getting to the carb but it did look like a significantly larger amount of fuel when compared to the other 2 cylinders. After closer inspection, when I turn the starter over trying to get the engine to kick I notice some fuel escaping the motor. I cannot tell from where, but I am leaning towards it sneaking out the fuel supply hose attached to the third carb. So the inside of the rear carb is getting (what appears to be) too much fuel, and some is leaking out as well. The third cylinder is not running, and the other two are, but they are running at high RPMs.

    I rebuilt the fuel pump and all of these issues are still occurring. Could it be that front and middle are running lean and not getting enough fuel and the rear cylinder has the right amount of fuel and its not starting for a separate reason? I am almost ready to give up because there are too many paths to chase.

    I am just starting this project back up after a long fall/winter in New England so this is not as fresh in my mind as it was last summer.

    Any ideas for a next step?


  2. #2
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    All of the cylinders run at the same rpm. They have to they are all on the same shaft.

    Do you have a spark tester? Have you verified spark to the rear cylinder?

    Not sure where you are saying the fuel is leaking out.

    Is the plug on the third cylinder fouled?

    Did you check pop-off for all the carbs? New parts?

  3. #3

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    i know they have to run at the same rpm, my point is it seems to be running high at idle, and idle plate is nearly closed.

    i have no checked pop off because i do not have the tool.

    i am going to put the slx carbs back on because that yielded the best behavior. from there i will confirm whether or not the rear cyl is still acting up.

  4. #4
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    Is this in the water or out of the water?

    My 780s all run about 2800rpm out of the water and around 1250 in the water.

    The super-rich carb may be opening the seat too soon.

  5. #5

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    Out of the water.

    The MFD is dead so I can't tell the RPMs. My induction tach sucks as well, I dont trust it.

    I put the slx carbs on and get the ski to run on every one of the cylinders and they all sound the same. Which is high. Might take it somewhere to get the carbs tuned. The fuel delivery seems to be of equal volume in all 3 cyl at this point.

  6. #6
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    You checked the fuse for the MFD?

    And tried a reset procedure?

  7. #7

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    The guy I bought it from rewired the cdi around it. I took the MFD apart and a component had blown. Totally fried and melted some plastic. The traces look ok so I could solder something in but then I'd have to rewire. Not something for this weekend.

  8. #8
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    That sounds like the voltage regulator or the diode that always seems to go.

    Fixable.

    I can't find my MFD repair thread...did they get nuked or archived?

  9. #9

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    if I take a picture, would you be able to confirm?

    any idea where i could source the failed parts if it is the voltage regulator or the diode like you suggested?

  10. #10
    Sooo...how much for the 780? stimpsonjcat's Avatar
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    picture of the damaged innards?

    maybe.

    Be very careful removing the outer edge to get the case open. I have managed to resurrect 2 MFDs, but I also ruined one by getting careless (well, never got a chance to fix it rather than ruined it...it didn't work anyway)

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