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  1. #1

    need help with my 1998 seadoo speedster twin 787's

    hey everyone, here is the problem i am having, the one engine on the passengers side runs great, the one on the drivers side is the one with the problem with, here what it is doing, and what i have replaced.....ok just bought this boat, and found out that the one motor was out of time, got a new rotary valve and timed it to 146.5-147, 64-65 degrees, put it back together and still didnt start, ripped it apart again and it was out of time again, to find out the brass gear was stripped, so i replaced that, did the timing again and now it will start with pouring gas down the carbs, and throttle wide open, then she will run but when i pull back on the throttle, down to idle or just before, she stalls, and wont start again until i pour more gas down the carbs, and wide open throttle again. now i have pull the pick up out of the tank and it is fine,pulled the fuel pump out, ripped it down, and it is fine, rebuilt the carbs, new fuel lines from tank to carbs, now i have done a pressure test from the crank cases, and when rolling over it has low pressure, but when started it has lots of pressure. this thing has me baffled, any info on what to look for, or check, please let me know.....

    thanks mike

  2. #2
    sounds like you have an air leak somewhere did you put the oring back on the rotary valve cover? If not that it could be a crankseal or base / head gasket if you can somehow pressurize the crankcase to 9 p.s.i with a mighty vac it shouldn't lose more then a lb a min if it does use soapy water to find the leak out of a spray bottle

  3. #3
    i have put an air hose to the lower crank case, and set it at 5 psi, and listen to see if any air was leaking out, and the only place i heard was coming out of the carbs, as for the rotary valve i put a new one in.

  4. #4
    ok i pressurized the crank case to 9 psi like you said, and started pouring soapy water over it, nowhere on the motor was it bubbling from the soapy water, oh and by the way i did a compression test on it also when i got it, 150 psi in each cylinder.

  5. #5
    I figured out the problem, all is good now, both engines run perfect

  6. #6
    big john's Avatar
    Join Date
    Sep 2010
    Cocoa Beach, Florida, United States
    tell us what it was !!!!!!!

  7. #7
    Sorry been away awhile, but to answer what was wrong, well where do I begin. After looking for air leaks, timing and fuel, I decided to pull the motor out, and rip it apart, well here is what I found, 1 all home made gaskets, top to bottom, 2 pistons put in backwards, it seems the guy before me figured he was a great mechanic and could fix it himself, boy was he wrong. Anyways I rebuilt it properly and she works great, now the only thing is I can only do 5500 Rpm in it and can't open it up, cuz it starts to bounce really bad.

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