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  1. #1

    1996 Seadoo XP - Chasing a Ghost - Stumbles and Sutters off idle

    Bought a 1996 XP that had been sitting for 3 years. Had issues (Replaced Cracked Coil, Replaced Starter, Went through pump w/new wear ring, etc). This is the 6th or so Seadoo 787 I have messed with (purchased, fixed, rode, sold).

    As with my past XP's, I paid particular attention to fuel / delivery. Drained tank and filled with fresh non-ethenol fuel. Replaced all the gray "tempo" lines with new colored poly lines. Removed carbs and cleaned filter screens, general inspection, reinstalled. Verified tank vents and fuel selector are working properly (using pop off pump). Boat has a primer set up on it / No choke plates (had to replace primer, as it was leaking).

    Boat fires up right away and idles fine. Give it a few minutes to warm up. Any more than a slight throttle and you get a bog. Won't die, will just sit and stutter. I have tried various low speed / high speed settings (seems to like Low at 1 turn out and High at about 1/2 - 5/8 ) and if I mess around with it long enough and it will eventually take off and run well for a while but die . . some times at speed. Then fire right back up. With all this said, I have actually had it run fine for a full ride (10 minuets or so) . . but same stuttering problem at the beginning if I even dry fire it on the trailer or trailer w/hose/fake lake. Not a confidence instilling boat.

    So I suspected that my "quick and dirty" carb clean was not sufficient. So I pull the carbs again and to go through them completely. Before I pull them apart I verify that the fuel pump seems pass the basic test (blow through inlet, can't suck through inlet . . . reverse for return line) . . . but both carbs fail to hold pressure for a pop off test. So thinking I have found the ghost . . . apart they come.

    I went through both carbs completely, right down to replacing the check valves (getting pretty good at these). Screw it all back together and still won't hold pressure. Use some soapy water and find both carbs are leaking from the fuel pump / check valve side of carbs, along the top surface of the gasket. After reinspecting, re-snugging down the screws still no pressure. On the third and more careful inspection I replace the odd shaped rubber o-ring type gasket with an extra Mukuni OEM version I had in inventory. Both carbs now hold pressure. Pop off right around 29-30 PSI (reused the spring that was in the carbs) . . . which according to several threads I searched . . . seems to be reasonable. At this point I question the SBT carb kit I bought. I have had such great luck with SBT starters, pump wear rings, etc . . . that I thought I would try a SBT carb kit.

    I reinstall carbs. Same problem (fires right up . . stutters off idle). At this point I bypass the fuel selector AND the Seadoo OEM fuel filter by using a new in line filter I had laying around and plumbing all this right to the "On" nipple of the fuel pick up. I have had the fuel pick up out of this boat previously and all looked sano. After all this . .. still no luck same problem (fires right up . . stutters off idle).

    Trying to gain more clues . . . I fire the boat up (still on trailer) and pay particular attention to the fuel in the poly fuel lines. The fuel filter never seems to fill completely . . I also only see a slight amount (line not full) flowing out of the return lines.

    So . . . after the above long preamble . . . attempt at diligence. . . here are my questions for you experts . . . . should I do the following, or do you have other ideas . . . . really struggling here to solve this one:

    1. Replace fuel pump (clear plastic gasket / rubber gaskets) with Mukuni OEM? I would prefer not to pull the carbs off the boat again, and I think I can get to the Mag carb pump plate and do this with carbs on the boat. Remember both of the carbs pop off tested fine.

    2. I did not replace the pulse line as it appeared to be in good shape (and black rubber, not TEMPO) . but I will replace this when doing #1 if that is the recommendation.

    3. According to my research, the jets in the carbs do not appear to be OEM sizes (might explain why the boat likes the High speed jet out 1/2 - 5/8 more than the factory recommendation of 0). Using my magnifying glass (eyes are getting old) what I think I read on BOTH carbs was 1.5 Needle/Seat; .75 (small); 1.25 (large) and again I have measured the Pop Off of between 28-30 PSI for both carbs. The previous owner said that he had spent $2K 7 years ago having Group K going through the motor (he was a military guy stationed at 29 Palms in CA). I question the story (no receipts / records). . but who knows. Given my preference NOT to pull the carbs all apart yet a third time . . . I am hoping the above is workable.

    I appreciate any guidance you can provide.

    Thank you.


  2. #2
    rhyne717xp's Avatar
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    The factory jetting is 70 pilots 142.5 mains with a factory flame arrestor. 80 gram springs 1.5 Needle Seats. For a x4 787. Reference the pop off chart to see what pop off should be. 30 psi may be a little low for a factory flame arrestor.

    Are u running after market Flame arrestors? You said there is a primer valve. If they are aftermarket, should be running 2.0 NS's with a 65 to 80 gram springs. The 75 pilots are fine but you probably need at least a 142.5 mains. Most of us use 145's high/75 low.

  3. #3
    Quote Originally Posted by rhyne717xp View Post
    The factory jetting is 70 pilots 142.5 mains with a factory flame arrestor. 80 gram springs 1.5 Needle Seats. For a x4 787. Reference the pop off chart to see what pop off should be. 30 psi may be a little low for a factory flame arrestor.

    Are u running after market Flame arrestors? You said there is a primer valve. If they are aftermarket, should be running 2.0 NS's with a 65 to 80 gram springs. The 75 pilots are fine but you probably need at least a 142.5 mains. Most of us use 145's high/75 low.

    Thank you. Those look to be the same general specifications I looked up earlier. Yes factory FA. Pop off chart (from OEM Seadoo Manual) is a is a bit of a joke . . 23 - 42 (if I recall correctly) . . most the threads I have researched say upper 20's is what to expect. . . but I am certainly open to other opinions.

    Are you saying you believe the problem I describe, will most likely be solved by upping the mains to 142.5? The stutter happens IMMEADIATELY off idle. According to the Mukuni tuning guides, the mains should have little material effect until later in the RPM range . . . but again I am certainly open to other opinions.

  4. #4
    rhyne717xp's Avatar
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    [QUOTE=kkosche;2129154]
    Quote Originally Posted by rhyne717xp View Post
    The factory jetting is 70 pilots 142.5 mains with a factory flame arrestor. 80 gram springs 1.5 Needle Seats. For a x4 787. Reference the pop off chart to see what pop off should be. 30 psi may be a little low for a factory flame arrestor.

    Are u running after market Flame arrestors? You said there is a primer valve. If they are aftermarket, should be running 2.0 NS's with a 65 to 80 gram springs. The 75 pilots are fine but you probably need at least a 142.5 mains. Most of us use 145's high/75 low.

    Thank you. Those look to be the same general specifications I looked up earlier. Yes factory FA. Pop off chart (from OEM Seadoo Manual) is a is a bit of a joke . . 23 - 42 (if I recall correctly) . . most the threads I have researched say upper 20's is what to expect. . . but I am certainly open to other opinions.

    Are you saying you believe the problem I describe, will most likely be solved by upping the mains to 142.5? The stutter happens IMMEADIATELY off idle. According to the Mukuni tuning guides, the mains should have little material effect until later in the RPM range . . . but again I am certainly open to other opinions.[.

    If you are running stock you are way too rich for low speed fuel circuit. The pop off for stock should be around 38 psi. I would jet to factory specs and try that. I would either run one size larger main in the pto or turn the high speed adjuster a 1/4 to 1/2 out. With the mag at 0 turns out. seadoo learned to do this on the 787 in 97/98. The pto runs a touch leaner from being the furthest from the fuel pump.

  5. #5
    rhyne717xp's Avatar
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    Set carbs to
    70 pilots
    142.5 pto 140 mag
    80 gram (black) springs with 1.5 N/S's
    Low speed 1 1/4 out
    High speed 0 out.

    You should be fine with a factory flame arrestor

  6. #6
    Quote Originally Posted by rhyne717xp View Post
    Set carbs to
    70 pilots
    142.5 pto 140 mag
    80 gram (black) springs with 1.5 N/S's
    Low speed 1 1/4 out
    High speed 0 out.

    You should be fine with a factory flame arrestor

    As stated in my previous message, "Yes factory FA."

    I have reviewed the factory specs before posting my message . . . you really believe by a slight spring and main change, my off idle symptoms will disappear? No concern about the fuel delivery (as I described in my original posting)?

    Sorry to be redundant . . but I am reluctant to pull everything apart a 3rd time, until we are reasonably certain we can identify a smoking guy for both the symptoms (off idle stutter) and the clues (fuel in return line).

    I appreciate your time and assistance.

  7. #7
    rhyne717xp's Avatar
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    75 pilots and lower pop off =Way too rich, causes loading up/stumbling off idle. There may be other issues as well.

    Sorry, but i do think you should follow factory specs on jetting. Get that right then you can eliminate that as a culprit and move on to solving the problem if that doesn't take care of it.

    The guy who had the ski before u may have had aftermarket flame arrestors and put the ski back to stock without changing the pop-off. Some people cut the springs in stock N/S's to lower pop off and try compensating with a larger pilot, so they don't have to spend money on 2.0's.

    Anyway, whenever trying to find a problem its always wise to put the ski back to oem specs. If you don't like pulling the carbs. I suggest putting back to stock specs and be done with carb jetting.

    Buy some new 80 gram (black) springs
    70 pilot X 2
    142.5 pto main 140 mag main

    You can run 140 mains in both but open up the pto 1/4 to 1/2 turn.

    The jetting has to be right or you could be overlapping another problem.
    Last edited by rhyne717xp; 03-24-2013 at 11:25 AM. Reason: Stupid smartphone

  8. #8
    Quote Originally Posted by rhyne717xp View Post
    75 pilots and lower pop off =Way too rich, causes loading up/stumbling off idle. There may be other issues as well.

    Sorry, but i do think you should follow factory specs on jetting. Get that right then you can eliminate that as a culprit and move on to solving the problem if that doesn't take care of it.

    The guy who had the ski before u may have had aftermarket flame arrestors and put the ski back to stock without changing the pop-off. Some people cut the springs in stock N/S's to lower pop off and try compensating with a larger pilot, so they don't have to spend money on 2.0's.

    Anyway, whenever trying to find a problem its always wise to put the ski back to oem specs. If you don't like pulling the carbs. I suggest putting back to stock specs and be done with carb jetting.

    Buy some new 80 gram (black) springs
    70 pilot X 2
    142.5 pto main 140 mag main

    You can run 140 mains in both but open up the pto 1/4 to 1/2 turn.

    The jetting has to be right or you could be overlapping another problem.

    Thank you. I will order as you recommend and report my findings. Your time is appreciated.

  9. #9
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    Have you checked for proper stator operation and ohmed it out? Is it putting proper voltage to the battery? Maybe it's electrical and not fuel related. 787 stators are known for giving problems.

  10. #10
    rhyne717xp's Avatar
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    I would jet to factory specs either way, but what myself says could be a factor as well. A bad charging system can cause problems as u described. The rectifiers can go bad and cause ignition problems. You can disconnect the yellow leads and see if this helps. If it runs fine then you may have a bad rectifier and/or stator. The poor jetting could be the problem or be part of.

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