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  1. #1
    barthel's Avatar
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    Question 750 STX Pump Issue (I THINK) Now with PICS!!!!!

    Hey all, Happy Independence Day!!!

    We had out ski's out on the lake today, both were doing good and both pissers worked (different thread). But, I encountered a problem I need some help with.

    I was riding the 750 about 15mph. There was some sort of clunk, then I totally lost thrust. I jumped in and check the intake grate, all was clear. Got back on and started it, everything seems fine until I give it some gas. The engine revs like normal and bubbles come out the back, but I don't go anywhere, there is literally NO thrust. My wife said it looked like all the water was coming out of the right side of the rear.

    Towed it back, put it up on the trailer, intake was still clear. I started it, shaft turns and impeller turns, but it seemed "klangy", like a marble being shaken inside a tin can.

    Any guesses? I imagine I'll be pulling the grate and the ride place, but am not exactly sure what I'm going to be looking for.

    Well, I pulled the ride plate, intake grate and venturi along with the stator vane cone. Everything looks OK except for a small chip off one of the impeller blades, which I can't imagine is causing this problem.

    Down the Vanes:


    and from the other side:


    There was a small chip in one of the impeller blades on the outlet side, but I can't imagine all this could be caused by that (although I could be wrong). The only other thing I noticed was a small amount (1/8 inch or so) of front to back play in the shaft, but no side to side movement.

    Any ideas?
    Last edited by barthel; 07-06-2011 at 10:54 PM.


  2. #2
    steve45's Avatar
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    Look at the drive coupling and see if there's anything wrong there. You'll probably end up pulling the pump.

  3. #3
    barthel's Avatar
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    I checked the coupling (visually), everything looks good. I'm trying (notice I say 'trying') to pull the pump as we speak.

  4. #4
    barthel's Avatar
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    UPDATE I

    Well, got the pump out. With the exception of the edges of the impeller looking a little rough (see previous pics) everything seems fine. The splines are in good shape, the PTO and coupler are solid, tunnel and venturi look good, from the look of it (which is all I have to go on at this point) everything seems to be within spec. The only thing I think I will do is take my Dremel and smooth out the pits on the impeller.

    Am I having an impeller issue? I REALLY need some help with this guys, I have NO clue what I'm looking for.

  5. #5
    steve45's Avatar
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    Don't know. Look at the stator vanes (the fixed vanes that are cast into the pump housing). You might also have an air leak somewhere.

  6. #6
    barthel's Avatar
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    I don't mean to sound dense, but where would it be leaking air from?

  7. #7
    steve45's Avatar
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    Well, it's not really air, but bubbles caused by turbulence. I like to use sealant all around where the pump mates with the pump shoe and intake grate. Check the condition of the rubber seal around the pump housing . Make sure the pump shoe is glued in securely and put sealant around the edges to smooth the flow.

    Keep in mind that the impeller will ring like a bell when it's out of the water. Each time a cylinder fires, it's like hitting the driveshaft with a hammer.

  8. #8
    barthel's Avatar
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    Thanks Steve.

    So based on the pics, will I need a new impeller or can I get by with the one I have? At this rate, I'm thinking of putting it all back together but re-sealing it, some of the silicone was old. Should I use marine silicone or Permatex?

    Also, is the shoe usually glued in? I couldn't see any bolts to take it off but did see sealant around the edges. Should I consider pulling it and re-gluing/re-sealing it?

  9. #9
    steve45's Avatar
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    The impeller looks good, you might smooth up the edges of the blades.

    Old or loose silicone should be replaced. Yes, the pump shoe is glued in. Don't try to remove it unless it's actually loose. Fill gaps around the edges with silicone sealant. 3M 4200 quick dry works good and is removable. Don't use 5200 or you'll never get it apart again.

  10. #10
    barthel's Avatar
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    Steve, are you the only one on the board???? =)

    Thanks for the info. I am going to smooth out the impeller edges with a dremel. My thought now is that some seal had to have given way even though I never saw anything. I'll get some of that 3M stuff and put it all back together and re seal it (after I remove the bolts that broke removing the pump, all 4 of them).

    Thanks for the help Steve.

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