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  1. #1

    Need help diagnosing 951 engine issue

    Hello,

    This is my first post, i 9have owned a number of seadoos in the past but never one with a 951 cc engine. A few weeks ago I bought a 1999 XP limited that wouldn't start. I checked the compression before making the purchase, the front cylinder was at 60 psi and the rear at 120. Got A great deal at $850 with a trailer.

    The previous owner was the second owner and it was his first pwc. According to him it ran on the trailer when he bought it but like crap when he got it to the water. He subsequently had the carbs rebuilt and it ran fine for a few minutes when he took it back to the water. During his first run it died and he hadn't touched it since. it has been sitting for about 7 months.

    When I got it home I found and removed nylon line wrapped around the drive shaft next to the through hull fitting. I also added stabilizer to the fuel and verified that Seadoo two stoke oil is in the tank. When I pulled the head I expected to see a burned up front piston but it looked fine and moves freely when I turn the engine over. The domes of the head look great too.

    I plan to take the ski into my local shop for diagnosis but would like to narrow down the possibilities before I do. If the cost to repair is over $1,000 I will sell it and the trailer otherwise I plan to refurbish the ski and add it to my fleet (I.e., 2010 Yamaha 242 LS, 2006 Yamaha Fx cruiser and 1996 Yamaha wave blaster 2).

    My neighbor used to own and maintain race karts and thinks the low compression may be caused by a bad crank seal. Any ideas on what could be causing the low compression are welcome and would be appreciated.
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  2. #2
    SURFnTURF's Avatar
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    Cant be the crank seal as compression is only in the combustion chamber area above the ports. Usually low compression is due to the rings not sealing adequately against the sides of the cylinder bores.Can be head gasket failure but very rare

  3. #3
    Sanfish's Avatar
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    Your pictures aren't detailed enough but just looking at the domes being all wet and dark. Next thing I would do it pull the reeds out and make sure they are well seated - pay close attention to the corners because thats where they typically start to edge out.

    Regardless, I'd just pull cylinder and send off for fresh bore. Buy some ProX pistons/rings and call it a day. Why not, its cheap and have little invested.

    Make sure you are running #170 main jet (1/4 out).

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  5. #4
    88kawi5fiddy's Avatar
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    New pistons and rings, and top end bearings, pull the motor, clean carbs and rear carb filter, pull tank and drain and clean it out well, and use new fuel lines.

    $500 or less repair. Easy.

  6. #5
    Quote Originally Posted by Sanfish View Post
    Your pictures aren't detailed enough but just looking at the domes being all wet and dark. Next thing I would do it pull the reeds out and make sure they are well seated - pay close attention to the corners because thats where they typically start to edge out.

    Regardless, I'd just pull cylinder and send off for fresh bore. Buy some ProX pistons/rings and call it a day. Why not, its cheap and have little invested.

    Make sure you are running #170 main jet (1/4 out).
    Thanks for all the replies guys. I think I'm going to go with the fullbore top end rebuild kit/service using pro x Pistons and have them modify the reed valves as well. What are you referring to in regard to the #170 main jet / 1/4 out ?

  7. #6
    Sanfish's Avatar
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    Quote Originally Posted by Lawgiver View Post
    What are you referring to in regard to the #170 main jet / 1/4 out ?
    The 951 uses Mikuni i46 carbs and as with all Mikuni carbs, have a low (pilot) and high (main) fuel jet. These motors came underjetted and going to a #170 gives a safety margin. The other thing to note is '99 was the first year of the "pumper" carbs where it squirts gas on initial trigger. While its okay if all the mechanicals that control the squirters work...often times are not working or improperly adjusted. So the hot setup is to remove the squiter setup and run a #95 pilot jet.

    The reference I made about "1/4 out" means you adjust the high speed screws 1/4 turns out from closed. You will adjust by doing a plug-chop - goal is color of cardboard.

    Oh, and follow 88kawi5fiddy suggestions about cleaning tank and running new fuel lines. BRP used terrible fuel lines that broke down causing issues. Rule of thumb is, if you see gray lines...get them out. The fuel lines on the 951 uses 5/16" lines (bigger than all other models of the time). Don't be tempted to run fancy colored clear fuel lines....they are all junk and will harden. Bottom line, DO NOT overlook your fuel lines!!

  8. #7
    Quote Originally Posted by Sanfish View Post
    The 951 uses Mikuni i46 carbs and as with all Mikuni carbs, have a low (pilot) and high (main) fuel jet. These motors came underjetted and going to a #170 gives a safety margin. The other thing to note is '99 was the first year of the "pumper" carbs where it squirts gas on initial trigger. While its okay if all the mechanicals that control the squirters work...often times are not working or improperly adjusted.... So
    Thanks again, got it I think. That is go with 170 on the mains, 95 on pilots and turn the high speed screws out an additional 1/4 turn from the stock settings on both carbs. I need to find out what the stock settings are (recall the carbs have been rebuilt recently already).

    I replaced all the gray fuel lines in the previous four seadoo PWCs I owned so know about the issue and plan to do the same here.

    Im not sure about the chopping my/cutting/cardboard color remark but think you mean cutting the spark plug lines back a little bit.

    I'm also rethinking taking this to shop and may do this myself, depends on how much information I can find here and elsewhere and how confident I am in it. I don't mind getting my hands dirty but am hesitant to put time and money into this ski when I have not even identified what the root cause(s) of the failure is or are. So first things first, I'm going pull the head (again) and the cylinders to pack them for shipping to fullbore and to hopefully Identify what went wrong. I welcome any alternative actions that the members of this forum (with experience) may suggest.

  9. #8
    Sanfish's Avatar
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    Quote Originally Posted by Lawgiver View Post
    That is go with 170 on the mains, 95 on pilots and turn the high speed screws out an additional 1/4 turn from the stock settings on both carbs. I need to find out what the stock settings are (recall the carbs have been rebuilt recently already).
    Thats not what I said. The 170 main is fine but ONLY DO THE #95 PILOT JET IF YOU REMOVE ACCELERATOR PUMP. Ski will run really bad if you put #95's and left pumps in place.

    Also, I said 1/4 turn out FROM BOTTOM. I didn't say 1/4 turn from stock.

    Quote Originally Posted by Lawgiver View Post
    Im not sure about the chopping my/cutting/cardboard color remark but think you mean cutting the spark plug lines back a little bit.
    No

    Plug chopping is a 2-stroke term for when you are trying to adjust carb fueling (screws and/or jets). Basically you run WOT pointed to shore and kill motor at WFO. Then pull plugs and read, color on the porcelain should be similar shade as carbboard. Obviously I'm simplifying the whole process because there is a little more to it then that. The hard part is timing it just right so you coast to shore and not run the ski 30FT up the beach. Then again, survival of the fittest

  10. #9
    Thanks for the clarification, I going back and forth on whether to take this to My trusted pwc mechanic or do it myself. I'm not motivated nor do I have the time to become a quasi Seadoo engine tech but I don't want to fix this more than once either. Tuning carbs has always been more of an art than science too me and I've never been good at it.

    I think I will take a closer look at the cylinders and Pistons with my local shop and have them inspect the rest of the ski/engine as well as give me estimates on what it will cost to put it back together and tune it up using fullbore's top end or the parts and related services he provides.

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