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  1. #1

    Exploded the Waterbox

    Need some brain power here.

    So here is the chain of events: A few months ago, I rebuilt the engine in the 00' GPR - ski would crank but it wouldn't start unless I sprayed some starter fluid in it. Figured it was the plugs and/cables. Replaced both of those - no changes. Thought it wasn't getting fuel - pulled the sending unit and bypassed the draw line in a cup of fuel. Still nothing. Thought it might be the carbs (which were very, very dirty) - rebuilt those. No change.

    After I put the carbs back on, packed the fuel lines, and cranked it - still nothing, but it was backfiring occasionally. My guess is the lack of combustion with fuel reaching the cylinders caused a buildup of vapors - and the entire plastic waterbox exploded into hundreds of pieces. AFT crank seal looks good still, luckily.


    Any thoughts on what is causing the lack of ignition? Or why the hell the box exploded if I dont have ignition!?


  2. #2
    silver93t's Avatar
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    Well for whatever reason seems like fuel isnt combusting in the motor and the fumes built up in the water box then ignited. This can be very dangerous. Did you pressure test the motor after you assembled it? Do a compression test? If compression is low enough it may not start and flood out. If you kept cranking its possible for the vapors to build up like that.

  3. #3
    improvised tmg97gp's Avatar
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    LoL, I have had that happen to me also. That was the main reason I changed to a free flow pipe.

  4. #4
    Happily Self-Employed WFO's Avatar
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    usually a backfire thru the exhaust is an ignition timing problem

  5. #5
    improvised tmg97gp's Avatar
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    It happed 5 years ago when I first got my 2000GPR. I just finished a rebuild of the engine and carbs. I believe it was a lean back fire, because i tried to start it and draw fuel thru the carbs at the same time. I was very lucky that it didnt blow the crank seals out or break any reeds.
    This time when i built my 2001GPR, i made sure all the carbs were full of fuel before I attempted to start it for the first time.
    No back fire.......
    My 2000 ski, i am still finding pieces of that water box to this day!!!

  6. #6
    If you replaced your cables... Then Extra double check for correct sequence of connections from cdi to coil to spark plug.

  7. #7
    Roger - all good points. Will check all of these. Purchasing a free flow to eliminate to risk of shattering plastic going everywhere.

    When I primed the ski (packed the fuel lines), I used a clear hose from a cup of gas, pulled the plugs, and turned it over until the suction stopped. Let it sit for a bit, then tried to start. It must be something with the ignition....that's the last thing I can think of!

  8. #8
    Happily Self-Employed WFO's Avatar
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    Lean back-fire is usually thru the intake... usually, but Ive blown a few water boxes off too

    Common timing issues include: sheared keyway, broken flywheel, bad ECU, twisted crankshaft

  9. #9
    Happily Self-Employed WFO's Avatar
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    Also always on first fire-up with dry carbs, crank-but do not prime-, until fuel is coming out of the return line. That way you have no air in the carbs for backfires or lean run away

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