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  1. #1
    machine722's Avatar
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    Not getting top speed

    I recently put a new stock 780 engine in my 97 slt 780 and its running well. The old engine melted a piston, so i did a full engine swap. I also fixed the mfd that hasn't worked for 3 years now. The engine is putting out full RPM at 6550 but im not getting the top end that I used to get out of it. A few years ago when the mfd worked it would top out around [email protected] 6500rpm. The mfd stopped working for a couple years so i never noticed a decrease in top end. In the process of pulling the pump off during the engine swap i noticed a few nicks in the prop. Would this account for the loss of approx 8mph on the top end? Or could It be something else. Also any tips for adjusting the carbs for premix, I put the blocking plate on the new engine to avoid melting another piston.

    Thanks


  2. #2
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    Are you sure the old engine melted the piston from an oiling problem, and not a lean burn?

  3. #3
    machine722's Avatar
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    No im not 100% sure. The middle cylinder had the melted piston. I went to premix just in case. I figured it couldn't hurt, I was going to ritchen up the mixture as well to avoid the possibility of running lean.

  4. #4
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    can you post a pic of the old piston?

  5. #5
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    If your impeller is knicked and dinged, chances are good that your pump stator is beat up too. Are any of the vanes cracked or have chunks missing?

    Also need to check clearance between the impeller and wear ring. It should be around 4 -10 thousandths with 20 being the service limit.

  6. #6
    machine722's Avatar
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  7. #7
    machine722's Avatar
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  8. #8
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    That's some serious carnage there.

    Piston skirt broken.

    Causes:

    excessive piston to cyl clearance
    foriegn material in engine
    sharp ports (ports not chamfered)
    hydrolocked engine

  9. #9
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    That looks brutal! Looks like its melted too. That's so bad I don't know what to think.

  10. #10
    machine722's Avatar
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    If the reason was hydro lock, why would it only happen to one piston? Also took them out again yesterday. Overall it ran good but when wide open I still am loosing a good 5-8 MPH. I'm turning 6650 rpm so i would assume it has something to do with the pump. I'm going to pull the pump off today and take a look at it. Also i'v noticed that the sound is alot different than it used to be when the pump leaves the water. It has alot higher of a pitch, wondering if anyone has experienced something similar?

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