1995 XP (717) Rotary Valve or Compression?

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  1. #1
    PWCToday Newbie
    Join Date
    Oct 2017

    1995 XP (717) Rotary Valve or Compression?

    Hello everyone,
    My name is Jeff and I'm from South Florida.

    I got a project 1995 XP (717) 3 weeks ago. It didn't run for an undetermined time (between 1-2 years) and I didn't get much information on it.

    Because of the lack of info, I decided to do the following before even starting it:

    - Check the compression (front 135 / Back 145) - Your advice on this 7% difference? Can you tell me the acceptable tolerance for this engine model?
    - Rebuilt the carbs and tuned them
    - Changed the tempo lines / New spark plugs gaped at 0.22
    - Lot of TLC and I think settings in general are correct as I am kind of a maniac.

    What I didn't do:
    I left the old battery (just gave it a charge)
    I left the fuel and oil as it seemed clean and the jet always stayed in a good environment (garage)

    This said, it runs like a charm when started and is really responding to the throttle handle.

    BUT I am facing a known issue: Easy start on the trailer but hard start on water. I need an easy 10sc to 15sc of cranking before having some results. I found online that the Rotary Valve or a bad compression could be the reason.

    I have 2 questions:
    1/ Is my compression really bad and could be the reason?
    2/ How come the rotary valve can be the guilty? I mean, it is a metallic plate setup on a gear and I don't understand how it can go wrong and lose its setting.

    Thank you very much for your answers

  2. #2
    Resident Guru hafweigthr's Avatar
    Join Date
    May 2009
    South Carolina

    Re: 1995 XP (717) Rotary Valve or Compression?

    For a 717 155/155 is stock with good cylinder and piston/rings. 10 % variance is acceptable between cylinders. 717/657/787 Skis will run at 135 psi compression but you can start seeing some poor starting and hesistation ,etc. the lower you go below say 130.

    Rotary valve timing should be dead on to operate properly. However dead on is really about +-2 degrees since there is gear backlash between the crankshaft/rotary valve mating gear. Having the rotary valve off by one tooth will definitely affect starting and loaded runability.

    Something scaring a rotary valve surface or too much rotary valve clearance will also cause hard starts.

    Being significantly out on timing or a bad scaring(port to port groove) on the motor side surface of the rotary valve will cause backfiring.

    For some reason I have seen several 717s have the rotary valve gear move on the crank which chews up this gear and will cause major mechanical timing issues.
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  3. #3
    PWCToday.com Is My Home Away From Home bills86e's Avatar
    Join Date
    May 2008

    Re: 1995 XP (717) Rotary Valve or Compression?

    I would say to run for awhile before any Comp checking, as been used a long time. The hard start symptom is from excessive RV clearance. You stated starting right up, but when put in water, nooooooooooo. This is a carburetor problem of too much air and not enough fuel. Your ski has duel carb, so syn at spec pop-off and must be each carburetor within + _ one psi of each other. At your elevation, you would set at middle number of your spec. Rebuild time would be compression 120 psi or so.


  4. #4
    PWCToday Guru
    Join Date
    Oct 2012

    Re: 1995 XP (717) Rotary Valve or Compression?

    did you use oem mikuni carb kits and did you replace the needles ?
    95 hx 787
    96 xp with miller motor
    92 gmc typhoon and 99 frc vette

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