95 seadoo xp running on hose engine "runaway" effect

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  1. #1
    PWCToday Newbie
    Join Date
    May 2018

    95 seadoo xp running on hose engine "runaway" effect

    I was running my 1995 seadoo xp on the hose and I was adjusting the idle screw(which is supposed to be 3000RPM out of the water) it had gotten up to around 3500RPM and I throttled it some and it revved up to around 4000RPM or so but then it held up there. And then after a bit(without pushing the throttle at all, it started going faster and FASTER! I WAS PANICKED! IT'S GOING TO EXPLODE! I pushed the power button, it KEPT GOING. I PULLED THE CHOKE IT KEPT GOING BUT THEN FINALLY DIED after about 5 seconds.

    Standing there, I asked myself.... WHAT HAVE I DONE?!

    turn's out it's not too uncommon for that to happen lol. The "runaway" effect. First time it happened to me but was probably because I had it at higher RPMs for an extend period of time.

    Anyways, here's what I need help with though. After that happened, and I took a moment to calm down. When I tried starting it again it seemed like the pto side carb was not putting any fuel out.

    I pulled the spark plugs( the pto side plug was dry, and the mag side plug was wet) and did a compression test(honestly expecting the pto side cylinder to be blown) both tested at 135 psi(same as they were before).

    Any idea's?

    might be an air leak somewhere, I will check the check valves in the fuel pump on the mag side carb later today to make sure they aren't cracked.

    How can I test the fuel pump to make sure the check values are not leaking air?

  2. #2
    Resident Guru JC-SuperJet's Avatar
    Join Date
    Jul 2013
    Cypress, TX

    Re: 95 seadoo xp running on hose engine "runaway" effect

    Bad Check Valves will only leak fuel not outside air as they are in a closed circuit (see Mikuni Manual cut-out sketch), unless the pump diaphragm is leaking or there are air bubbles in the fuel line prior to the carb fuel inlet.

    If check valves lay flat and they are not creased, they are good. And the rubber holding grommets are not pierced.

    Do a pop-off test to see if the Needle Valve is leaking. It will also show any leaks in the fuel pump(very rare).

    Best to rebuild the carburetors. Do an air leak down test on the engine.

    Next time you have a run-away engine, hold the Stop button down while at the same time holding the throttle wide-open. Works every time.

    Another way is to stuff a rag in the exhaust outlet, a 100% choke.
    Last edited by JC-SuperJet; 06-14-2018 at 02:27 PM.

  3. #3
    PWCToday Newbie
    Join Date
    May 2018

    Re: 95 seadoo xp running on hose engine "runaway" effect

    some not so good news after that runaway... Things have gotten weird.

    so I did a compression check as a mentioned before, both cylinders are up at 135 psi(same as before the runaway)
    But now it is not running...

    like a mentioned, I could not see gas coming out of the rear carb looking down the intake(however, I did verify gas was coming out of the return outlet on it).
    Thinking that it must need some gas on the rear carb, I poured some gas straight down the rear carb. Results got messy here... It gave a fire punch here and there but for the most part just cranked with no fire. So I tried it a few times, still same thing.... I am stumped.... opened idle a little more tried pumping throttle some while cranking.

    Any ideas?

    I would think it would give me a little fire! even if carbs are messed up, if I'm pouring gas straight in, you know?

    My fear is that there is something wrong with the magneto, or something else, I have an inline ignition tester and I see spark on it, but could spark plugs still be bad? could it be due to an air leak in the lower end?

    Also, don't tell anyone I told you this, because I don't know when it got there, but... I found a washer down in the intake by the roatary valve opening. After the runaway I took the carbs our and cleaned them that night, I wonder if that's when that washer go in there... otherwise I don't know how it would have been running so well before? I did a check by hand reaching into the intake with my finger and then cranking, I lost my finger to the rotary valve!

    just kidding about losing a finger, but I did check with my finger turning the fly wheel by hand and seeing when the mag piston was as high as it could go the rotary valve seemed to be in the right position(or atleast close) from my aprox. turning guess from what the shop manual says.

    After the runaway, turning in the engine almost seems "loose" now? like when cranking it will give a few extra puffs than I think it did before? any idea's what might be going on there? both cylinders still have the same compression as before...

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