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  1. #1

    Exclamation Seadoo over-revving out of control

    Hi everyone. Having just purchased a XP Ltd '99 that was rebuilt 2 years ago and has sat around ever since, I'm having a few problems. It ran fine on the lake for a hour before it started bogging down between 2.5k and 4k revs. Came to the conclusion that the fuel lines/carburetor was blocked so I pulled the carby apart and filters were all blocked.

    Cleaned the carby out and put it back together. However I now have another problem. It seems to run ok (out of the water), but if I rev it past 4000rpm it takes on a life of it's own and revs way past the rev limiter (over 8000rpm) and you can't stop it unless you turn the fuel off, pretty scary! If you keep revs under 4000rpm it seems to be ok.

    So my question is, what did I screw up when I put the carburetor back together? Something to do with the main jet? Thanks!!


  2. #2
    mac_man_luke's Avatar
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    sounds like the butterfly is getting jammed open

  3. #3
    big john's Avatar
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    the 951 motor will do that, just pull the choke and will come right down to idle, mine has done it several times, had me baffled till i read somewhere that its a inheret trait of the 951 motor

  4. #4
    GGG's Avatar
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    That means its running lean. you either have a vacuum leak, your screens are clogged again or your jets are clogged

  5. #5
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    It basically a run away, kinda diesel's itself like that with whatever amount of fuel is in the bowls. Can be scary when it happens, especially if it goes for a long time, it will suck any oil out of the lines because the oil pump is not opening and it could seize...

    Caused by a slight airleak between carb and reed plate is usually it.

    If that happens, just hold the throttle open all the way. This will flood it with too much air and choke it out...

  6. #6
    Quote Originally Posted by GGG View Post
    That means its running lean. you either have a vacuum leak, your screens are clogged again or your jets are clogged
    No; Big John is right. 951's run lean at off idle due to the way the carbs are designed, so if you rev it up to 4K on the hose, many of them runaway without any other air leaks. However, it would be prudent to make sure that you don't have a carb base gasket leak, a reed to case leak, or a pulse line leak. Any leaks at these spots will make the problem worse.

    If you check it all out and have no leaks, if it happens again, just pull the choke or give it full throttle and it will die.

  7. #7
    Wrench's Avatar
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    Ive seen 2 951's do this and eventually melt the mag piston down. Its one of the check valves in the the fuel pump on the mag carb. Pull the fuel pump apart and check the clear check valves; 2 out of 2 times one of them was cracked which leans the mixture and causes them to run away or "diesel".

  8. #8
    I've just taken it out on the water and it didn't seem to do it, once you drop revs from 6k it comes down without too much hesitation. So maybe its just a 951 engine thing? Or should it not do it at all on the hose?

    Quote Originally Posted by Wrench View Post
    Ive seen 2 951's do this and eventually melt the mag piston down. Its one of the check valves in the the fuel pump on the mag carb. Pull the fuel pump apart and check the clear check valves; 2 out of 2 times one of them was cracked which leans the mixture and causes them to run away or "diesel".
    Which check valves are you referring to or what do they look like? I have the Seadoo manual here if it helps.

    Another problem I'm having (possibly related) is it bogging down between 2500rpm and 4500rpm. It bogs down and tries to die, and starts surging etc (as if not getting enough fuel). If you rev it above 4500rpm its goes like hell (running lean?). This is the reason I rebuilt the carb in the first place, but its still doing it. Any ideas, apart from the possibility of fuel hose blocked?

  9. #9
    Wrench's Avatar
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    ok then look in your manual, if you just rebuilt the carbs your should know what the check valves are. They are clear circles the size of the dime. Take the fuel pump off the mag. side carb and look. It wont run away in the water but its still running that cylinder lean (if thats the problem) and will eventually melt that piston and ruin the crank and connecting rod bearings. Which i am having to replace on mine now. VERY PRICEY. So take your carbs apart and check. Stop running it.

  10. #10
    Quote Originally Posted by RyanNZ View Post
    I've just taken it out on the water and it didn't seem to do it, once you drop revs from 6k it comes down without too much hesitation. So maybe its just a 951 engine thing? Or should it not do it at all on the hose?



    Which check valves are you referring to or what do they look like? I have the Seadoo manual here if it helps.

    Another problem I'm having (possibly related) is it bogging down between 2500rpm and 4500rpm. It bogs down and tries to die, and starts surging etc (as if not getting enough fuel). If you rev it above 4500rpm its goes like hell (running lean?). This is the reason I rebuilt the carb in the first place, but its still doing it. Any ideas, apart from the possibility of fuel hose blocked?
    Runaway only happens with no load on the engine, it will never happen in the water.

    Based on your lean mid-range, it does sound like you have carb issues or an air leak. It may not be the carburetor, it could be just about anywhere; carb gaskets, reed sealing surface, cyl base gasket, crank seal, case halves. You may need to pull it and do a pressure check....

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